Re: [time-nuts] Another atomic clock question
Some clarifications on the ADC in the ATmega328 and how it is used in the Arduino GPSDO. The resolution is 10 bits but you can select Vref. In my Arduino GPSDO it is set to the internal Vref = 1.1V so 1LSB is 1.1mV. From the beginning I used 5V as Vref but if you plot the response from the RC-net you find that the useful ADC range is only a fraction if you want to have a reasonable linearity. In the beginning I used only 600 out of the 1024 but still the time per bit was more than a factor two different. If somebody want to experiment with other processors for theTIC, a Teensy with 16bit ADC´s is probably a good idea because you can use only part of the range but still have good resolution (noise is another thing that may be both good and bad in a GPSDO). According to the datasheet the minimum conversion time is 65uSec for the ATmega328 (ADC clock max 200 kHz and 13 clock cycles). The discharge of the 1nF is not 1sec but 1mSec. If it was 1sec, 63% of the previous charge should be left and giving errors up to 63%. My assumption when designing the network was to have at least ten time constants of discharge before the next PPS. So a 100mSec time constant would be fine for that. The problem is that with a 1nF capacitor I would need 100Mohm as discharge resistor. To get 1.1mV (1nS) over 100Mohm you only need 11pA for example from the ADC input leakage current. I decided for 1Mohm that gives 1mv for 1nA. This gives the TIC a drift of about 1ns per nA change. Remember I wished to keep the drift to maybe 1nSs for a couple of degrees room temp change so the drift of the leakage current needs to be below say 0.5nA per degree. My practical testing has showed that I have about 1.2ns drift for 5°C change and it seems consistent between different Arduinos I have. The 1mSec time constant gives a discharge that directly after the pulse from the HC4046 ends is about 0.1% per uSec. So for a 65uSec delay the drop is about 65nS for a 1000nS reading and 32uS for a 500ns reading. If the delay is exactly the same every time it should be possible to compensate for. I have got indication that crosstalk between ADC channels may be a problem in the ATmega328 but with the single TIC and very slowly changing values on the other ADC channels I can´t say it is a problem for me. I also would encourage you to test both the Arduino dual TIC and using both halves of the HC390 whatever I have said about risks. The HC390 is probably not a problem at all for the nS readings as you and Magnus says. Lars Chris wrote: Let's see what is needed. The ADC is 10-bits so it can read to one part in 1024. It's a 5 volt full scale so we are only able to measure 5 millivolt increments The uP runs about 16 million instructions per second. What if we wait 1000 instructions to read the ADC what will the error be? The 1000 number is conservative by at least a factor of 10. The discharge resister has (assume) a one second time constant. The read delay would be 1000/16,000,000 or 63 uSec. in that time the voltage would have changed about 300 microvolts. The change is about 15 times less then the DAC is able to measure.But because of the conservative estimate it might 150 times to small to measure. So randomly delayed reads of the ADC will not matter. That said I'm sure we can do 100X better then the 63 uS estimate. On the other side, charging the cap. Let's say I mis-measured a wire and it is 1cm longer then I though. The added delay adds a tiny delay but this is not going to show up in a 10-bit ADC. Same if the propagation delay changes through the 74HC390 based variable loading of other output pins or noise from the 78ls05 voltage regulator. The DAC is set up for 5 mV steps. I just don't need to worry about errors that are well under 0.5 mV. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi Hal Not arguing for or against sawtooth or hanging bridges, etc. My needs for GPSDO performance are unquantified but likely quite modest. I just want to get something working that's a bit better than my OCXO. I don't think I need the sawtooth stuff to get started. Thanks jim ab3cv Date: Fri, 07 Mar 2014 21:28:31 -0800 From: Hal Murray hmur...@megapathdsl.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: hmur...@megapathdsl.net Subject: Re: [time-nuts] Another atomic clock question Message-ID: 20140308052831.40d3e406...@ip-64-139-1-69.sjc.megapath.net Content-Type: text/plain; charset=us-ascii j...@jtmiller.com said: I may switch the GPS module at a later date to one which provides sawtooth info if I really feel the need and add a delay line. Frankly I think I'll never get around to it. One nasty problem with hanging bridges is that if you don't believe in them, then you won't setup your monitoring system to notice them. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
I think the hardware delay line approach is the only solution for a simple D FF lead/lag phase comparator. It would be placed ahead of the FF. Which GPS being built now provide sawtooth info? 73 jim ab3cv ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Every timing GPS receiver has the sawtooth information: uBlox, iLotus, SkyTraq, Trimble just to name someone. On Fri, Mar 7, 2014 at 2:25 PM, Jim Miller j...@jtmiller.com wrote: I think the hardware delay line approach is the only solution for a simple D FF lead/lag phase comparator. It would be placed ahead of the FF. Which GPS being built now provide sawtooth info? 73 jim ab3cv ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
As I am a poor programmer and also lazy (includes hardware and software), I would like to ask the following question: How much better would a GPSDO like the Arduino GPSDO be with added sawtooth correction? Let’s say we assume the 1ns resolution TIC is perfect, no jitter from the uP and the DAC have a perfect frequency setting resolution of 1E-13. The receiver in my case is a M12 set in position hold mode after a survey and my measured ADEV starts at 2E-8 for 1sec and is 2E-11 at 1000secs. The MDEV is 2E-8 at 1sec and 2E-12 at 1000sec (very similar to what found on the leapsecond.com M12 page). The oscillator is my “8663”-type OCXO that I have measured to have an ADEV just above 1E-12 over the range 1-1secs. Let’s say the oscillator is perfect at 2E-12 over 1-1secs. The Arduino GPSDO control loop works as follows, as far as I understand, if set to a time constant =1000secs and damping =2 : TIC value is pre-filtered similar to an RC filter with 250seconds time constant (I like to refer to analog RC-filters being an RF and analog engineer) The filtered TIC value is divided by the time constant 1000 and adjusts the DAC proportional to this. The filtered TIC value integrates the DAC value after dividing it by (time constant * time constant * damping) = (/1000/1000/2). My explicit question is how much better the ADEV of the GPSDO oscillator output will be with sawtooth correction added in the software? Another question is how much better the ADEV will be if the TIC had a resolution of 0.1nsec instead? Maybe a third question could be if the DAC only had 1E-12 resolution? Is some more important factors needed to be known to calculate this to a reasonable accuracy? e.g. room temperature variations of the M12. In my own measurements, with about the same conditions as above with a time constant of 1000s, I got an output ADEV of about 3E-12 at Tau 1000s measured with an HP5370 against an LPRO Rb (plot was attached to Arduino GPSDO thread Feb 12 2014). This value looks very similar to the combination of the 1PPS MDEV and OCXO ADEV. Is that just a coincidence? Lars ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Fri, Mar 7, 2014 at 5:25 AM, Jim Miller j...@jtmiller.com wrote: I think the hardware delay line approach is the only solution for a simple D FF lead/lag phase comparator. It would be placed ahead of the FF. Simple? You are going to need a micro controller and software to (1) tall the GPS to output the sawtooth function, they don't typically output it untell you tell it to. then (2) recover the sawtooth function from the serial data. Then(3) convert it to the counts that units used in the delay line. Finally (4) you need to interface the delay line to the processor and send the current sawtooth function value over that interface once per second. Also when I do stuff like this I always want some kind of LCD display or at least blink LEDS so I know what's going on inside and then it is at least running. Your simple analog devices no longer a simple analog device. Do a full up parts count for both designes. I think the digital correction comes in lower. Both solutions need the same micro controller and it's support circuitry. As to which GPSes send sawtooth. It's a common feature but typically you need to enable it, the same way you'd enable a self-survey or set a minimum elevation angle or whatever. Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
I have quite often seen the simple D FF lead/lag phase comparator mentioned but not found any practical implementation in a GPSDO. Has anyone a schematic and hopefully real data? What is the performance? Is it better than a conventional GPSDO with a TIC+uP+DAC or is it only simpler? Lars On Fri, Mar 7, 2014 at 2:25 PM, Jim Miller j...@jtmiller.com wrote: I think the hardware delay line approach is the only solution for a simple D FF lead/lag phase comparator. It would be placed ahead of the FF. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
I'm new at this obviously. I was just looking at the uBlox-6 info and I don't see where in the NMEA sentences the sawtooth info is contained. Is it a manufacturer specific option that needs be turned on? Or is it contained within a standard NMEA sentence somewhere. I also didn't see it mentioned in the uBlox u-Center software users guide. Thanks Jim ab3cv Message: 3 Date: Fri, 7 Mar 2014 16:26:35 +0100 From: Azelio Boriani azelio.bori...@screen.it To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Another atomic clock question Message-ID: cal8xpmmstyj2gczpdimzr1bqbhavq4a6r0kjtwaal521t+6...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 Every timing GPS receiver has the sawtooth information: uBlox, iLotus, SkyTraq, Trimble just to name someone ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
j...@jtmiller.com said: I'm new at this obviously. I was just looking at the uBlox-6 info and I don't see where in the NMEA sentences the sawtooth info is contained. Is it a manufacturer specific option that needs be turned on? Or is it contained within a standard NMEA sentence somewhere. I also didn't see it mentioned in the uBlox u-Center software users guide. NMEA doesn't cover sawtooth. You have to shift to the vendor's proprietary/binary protocol. Also, you have to get the timing version of the firmware. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Chris, about using one Arduino for two GPSDO controllers: Even if a microcontroller has lots of capacity I would recommend to use separate controllers for each oscillator. One of the reasons is what Tom van Baak said about using only one interrupt to avoid jitter and even if you trigger both channels from the same PPS and have just one interrupt you will have a problem that you can´t read two ADC´s at the same time. Even the HC390 I wouldn´t use for two different oscillators to prevent crosstalk. Both the processor and HC390 is so cheap it isn´t worth the risk IMO. Actually I would also recommend to put them in separate boxes even if it is more work (and I´m lazy ) to get best performance. Having two GPSDO´s that you can compare is very nice as long as you understand how they correlate , if that is not what you want to test. Of course you can also set one or both in hold mode to test them freerunning. I have thought of connecting the M12 to the Arduino and if someone can help with code to get the sawtooth correction value into the Arduino and decoded I would be glad to have it. Lars From: Chris Albertson On Wed, Mar 5, 2014 at 5:43 PM, Didier Juges shali...@gmail.com wrote: Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Here is my plan for processing saw tooth data. If it's not going to work I'd rather hear about it now then a month from now after I've put in some effort. This is going into Lars' Arduino based GPSDO. Every second I read the voltage on a TIC capacitor. This tells by the phase in nanoseconds between the PPS and the OCXO. Then I add whatever the current GPS sawtooth value is to whatever my TIC said. I compare this to a set point. This is the phase error. The OCXO is adjusted based on a filtered version of this error. So in short, I don't correct even try to delay the pulse. I don't see any need to do that. I measure the pulse and get a number in nanoseconds. then I use sawtooth to correct the number. It seems way-hard and with no purpose to correct the pulse and then measure it. Better to correct the measurement. I think it is more accurate too a delay could never be perfect. The controller has LOT of spare capacity so I don't see way I can't add one of more TIC channels and a few more DACs I should be able to discipline an OCXO and my Rb oscillator from the same GPS PPS input. The 74HC360 is only 1/2 used an Arduino has enough spare pins. Any one more 74HC4046 and some passive parts would be required to build a dual channel GPSDO. It will be interesting to look at andompare the 10MHz outputs of two oscillators that are being disciplined by the same controller and GPS receiver. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Fri, Mar 7, 2014 at 9:57 AM, Jim Miller j...@jtmiller.com wrote: I'm new at this obviously. I was just looking at the uBlox-6 info and I don't see where in the NMEA sentences the sawtooth info is contained. There is no NMEA sawthooth sentence. You typically have to put the serial data output into binary mode. NMEA is a lowest common denominator data format used by GPS, marine autopilots, compass, wind and log instruments. It was never designed for timing. It's for ship and boat instruments. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Fri, Mar 7, 2014 at 10:28 AM, Lars Walenius lars.walen...@hotmail.com wrote: Chris, about using one Arduino for two GPSDO controllers: Even if a microcontroller has lots of capacity I would recommend to use separate controllers for each oscillator. One of the reasons is what Tom van Baak said about using only one interrupt to avoid jitter and even if you trigger both channels from the same PPS and have just one interrupt you will have a problem that you can´t read two ADC´s at the same time. You don't have to read both at the same time. All you need is to have a constant time between the interrupt and when you read the ADC. That constant can be any reasonable number so long as it remains constant Even the HC390 I wouldn´t use for two different oscillators to prevent crosstalk. Both the processor and HC390 is so cheap it isn´t worth the risk IMO. Risk? It's easy to measure. Risk is when you don't know what is going to happen. But in this case we can test. Actually I would also recommend to put them in separate boxes even if it is more work (and I´m lazy ) to get best performance. I think you might be addressing pico seconds on a system that works in the few nano seconds range.A serial commanded Rb oscillator moves in such large steps that I'm 100% sure the step quantization error will dominate everything. The step size is something like 5E-11. But the stability I expect will be very good. Having two GPSDO´s that you can compare is very nice as long as you understand how they correlate , if that is not what you want to test. Of course you can also set one or both in hold mode to test them freerunning. I have thought of connecting the M12 to the Arduino and if someone can help with code to get the sawtooth correction value into the Arduino and decoded I would be glad to have it. I'm looking for an OCXO. Not much reason to start before I find one. People are over bidding on eBay for 30 year old salvage parts. eventually I'll win one at a reasonable price. Then I'll write up my results. In the mean time I've started a wholesale refactoring of the posted Arduino code. I need t make it a bit more modular and testable. I have an Motorola Oncore UT+ type GPS. I think it might have the same sawtooth.I'm pretty sure there is code in the standard NTP distribution to read the Oncore type data and (maybe sawtooth???) I plan to read the NTP drivers and borrow whatever is usable. I did just build and finish testing a serial interfaced LCD display. Now I can display states using just two Arduino pins. (Without the serial interface an LCD takes 6 to 10 pins) I'm using I2C so I can add other devices to the same serial interface, like a DAC or whatever Lars From: Chris Albertson On Wed, Mar 5, 2014 at 5:43 PM, Didier Juges shali...@gmail.com wrote: Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Here is my plan for processing saw tooth data. If it's not going to work I'd rather hear about it now then a month from now after I've put in some effort. This is going into Lars' Arduino based GPSDO. Every second I read the voltage on a TIC capacitor. This tells by the phase in nanoseconds between the PPS and the OCXO. Then I add whatever the current GPS sawtooth value is to whatever my TIC said. I compare this to a set point. This is the phase error. The OCXO is adjusted based on a filtered version of this error. So in short, I don't correct even try to delay the pulse. I don't see any need to do that. I measure the pulse and get a number in nanoseconds. then I use sawtooth to correct the number. It seems way-hard and with no purpose to correct the pulse and then measure it. Better to correct the measurement. I think it is more accurate too a delay could never be perfect. The controller has LOT of spare capacity so I don't see way I can't add one of more TIC channels and a few more DACs I should be able to discipline an OCXO and my Rb oscillator from the same GPS PPS input. The 74HC360 is only 1/2 used an Arduino has enough spare pins. Any one more 74HC4046 and some passive parts would be required to build a dual channel GPSDO. It will be interesting to look at andompare the 10MHz outputs of two oscillators that are being disciplined by the same controller and GPS receiver. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris
Re: [time-nuts] Another atomic clock question
On 3/7/14 12:31 PM, Chris Albertson wrote: On Fri, Mar 7, 2014 at 10:28 AM, Lars Walenius lars.walen...@hotmail.com wrote: Chris, about using one Arduino for two GPSDO controllers: Even if a microcontroller has lots of capacity I would recommend to use separate controllers for each oscillator. One of the reasons is what Tom van Baak said about using only one interrupt to avoid jitter and even if you trigger both channels from the same PPS and have just one interrupt you will have a problem that you can´t read two ADC´s at the same time. You don't have to read both at the same time. All you need is to have a constant time between the interrupt and when you read the ADC. That constant can be any reasonable number so long as it remains constant there are plenty of Arduino-like boards out there that have ADCs triggered by the timer, which also fires the interrupt, but you don't have to worry about reading the ADC late. The teensy3.1 (new version of the teensy3 from PJRC) has a dual ADC, which can simulataneously sample. I've run the teensy3 at 300ksps+ (48 MHz processor clock). Right now, I've got software that is interrupt driven at 50 kHz that does two adc reads in a row and then feeds a 2 stage CIC decimator chain. It consumes about 60% of the processor, the bulk of which is the actual ADC read and the first integrators. for $20, it's hard to beat.. the only downside is that you can't go down to radio shack and buy one on the spur of the moment. They'll also do a not very optimized fixed point 128 point FFT in about 0.9 milliseconds: N pts μs 128 897 64 402 32 175 16 82 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Fri, Mar 7, 2014 at 12:57 PM, Jim Miller j...@jtmiller.com wrote: I'm new at this obviously. I was just looking at the uBlox-6 info and I don't see where in the NMEA sentences the sawtooth info is contained. u-blox calls it (Time)Pulse Granularity (PG). You're looking for the UBX clock info sentence which is proprietary so it starts with a P ($PUBX,04 in this case). It's a polled sentence It's in the GPS.G6-SW-10018-F document. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
jim...@earthlink.net said: for $20, it's hard to beat.. the only downside is that you can't go down to radio shack and buy one on the spur of the moment. At that price, you can keep a couple on the shelf. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi You can put the LEA-5T or the LEA-6T into a mode where they put out the sawtooth information on auto pilot. Once you get it set up (which you do each time you boot) it just keeps going. You must have the T version of the modules to get the sawtooth out of them. Bob On Mar 7, 2014, at 4:10 PM, Paul tic-...@bodosom.net wrote: On Fri, Mar 7, 2014 at 12:57 PM, Jim Miller j...@jtmiller.com wrote: I'm new at this obviously. I was just looking at the uBlox-6 info and I don't see where in the NMEA sentences the sawtooth info is contained. u-blox calls it (Time)Pulse Granularity (PG). You're looking for the UBX clock info sentence which is proprietary so it starts with a P ($PUBX,04 in this case). It's a polled sentence It's in the GPS.G6-SW-10018-F document. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Let's see what is needed. The ADC is 10-bits so it can read to one part in 1024. It's a 5 volt full scale so we are only able to measure 5 millivolt increments The uP runs about 16 million instructions per second. What if we wait 1000 instructions to read the ADC what will the error be? The 1000 number is conservative by at least a factor of 10. The discharge resister has (assume) a one second time constant. The read delay would be 1000/16,000,000 or 63 uSec. in that time the voltage would have changed about 300 microvolts. The change is about 15 times less then the DAC is able to measure.But because of the conservative estimate it might 150 times to small to measure. So randomly delayed reads of the ADC will not matter. That said I'm sure we can do 100X better then the 63 uS estimate. On the other side, charging the cap. Let's say I mis-measured a wire and it is 1cm longer then I though. The added delay adds a tiny delay but this is not going to show up in a 10-bit ADC. Same if the propagation delay changes through the 74HC390 based variable loading of other output pins or noise from the 78ls05 voltage regulator. The DAC is set up for 5 mV steps. I just don't need to worry about errors that are well under 0.5 mV. If I were building this using a 24-bit ADC and wanted to take full advantage of its resolution then tiny things matter. On Fri, Mar 7, 2014 at 12:47 PM, Jim Lux jim...@earthlink.net wrote: On 3/7/14 12:31 PM, Chris Albertson wrote: On Fri, Mar 7, 2014 at 10:28 AM, Lars Walenius lars.walen...@hotmail.com wrote: Chris, about using one Arduino for two GPSDO controllers: Even if a microcontroller has lots of capacity I would recommend to use separate controllers for each oscillator. One of the reasons is what Tom van Baak said about using only one interrupt to avoid jitter and even if you trigger both channels from the same PPS and have just one interrupt you will have a problem that you can´t read two ADC´s at the same time. You don't have to read both at the same time. All you need is to have a constant time between the interrupt and when you read the ADC. That constant can be any reasonable number so long as it remains constant there are plenty of Arduino-like boards out there that have ADCs triggered by the timer, which also fires the interrupt, but you don't have to worry about reading the ADC late. The teensy3.1 (new version of the teensy3 from PJRC) has a dual ADC, which can simulataneously sample. I've run the teensy3 at 300ksps+ (48 MHz processor clock). Right now, I've got software that is interrupt driven at 50 kHz that does two adc reads in a row and then feeds a 2 stage CIC decimator chain. It consumes about 60% of the processor, the bulk of which is the actual ADC read and the first integrators. for $20, it's hard to beat.. the only downside is that you can't go down to radio shack and buy one on the spur of the moment. They'll also do a not very optimized fixed point 128 point FFT in about 0.9 milliseconds: N pts μs 128 897 64 402 32 175 16 82 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 3/7/14 3:33 PM, Chris Albertson wrote: Let's see what is needed. The ADC is 10-bits so it can read to one part in 1024. It's a 5 volt full scale so we are only able to measure 5 millivolt increments if you use the teensy3 it has a 16 bit ADC with realistically, about 13 bits performance. The teensy3.1 has a 12 bit DAC, but since I haven't got one in my hot little hands yet, I don't know the performance. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi With a “real” 12 to 13 bit ADC and a 200 ns TDC pulse you would ideally get 200 / 4096 as your LSB. Nothing like this is ever perfect, so you probably aren’t going to get 50 ps. You probably will be below 100 ps. That’s plenty good enough to make sawtooth correction useful. Bob On Mar 7, 2014, at 6:38 PM, Jim Lux jim...@earthlink.net wrote: On 3/7/14 3:33 PM, Chris Albertson wrote: Let's see what is needed. The ADC is 10-bits so it can read to one part in 1024. It's a 5 volt full scale so we are only able to measure 5 millivolt increments if you use the teensy3 it has a 16 bit ADC with realistically, about 13 bits performance. The teensy3.1 has a 12 bit DAC, but since I haven't got one in my hot little hands yet, I don't know the performance. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hello David, Not sure what is wrong here - I still can't reach it. If it isn't too much trouble - can you send me a screen shot off-list - I can look up the patents as long as the numbers are listed. Thanks! John W. j...@westmorelandengineering.com On Thu, Mar 6, 2014 at 11:09 PM, David J Taylor david-tay...@blueyonder.co.uk wrote: To the Mike that posted: http://www.pst.netii.net/patents.htm - I tried going to your site - can't reach it. Is the site operational? I wanted to take a look at your patents. Thanks, John Westmoreland == Jon, It's working OK from Edinburgh at 07:08 UTC. David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Fri, Mar 7, 2014 at 5:45 PM, Bob Camp li...@rtty.us wrote: You must have the T version of the modules to get the sawtooth out of them. Per the documents (and M Tharp) you don't need a T model to get quantization correction (I only have a T so I don't have first-hand information). I understand this is also the case with the NEO models as well. In the LEA-6 generation only T models provide RTK data, dual Timepulse and support Time Mode which is what they call a stationary antenna with high quality position information. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi On the 4’s and 5’s you only got a pulse + correction with the T model. Bob On Mar 7, 2014, at 8:06 PM, Paul tic-...@bodosom.net wrote: On Fri, Mar 7, 2014 at 5:45 PM, Bob Camp li...@rtty.us wrote: You must have the T version of the modules to get the sawtooth out of them. Per the documents (and M Tharp) you don't need a T model to get quantization correction (I only have a T so I don't have first-hand information). I understand this is also the case with the NEO models as well. In the LEA-6 generation only T models provide RTK data, dual Timepulse and support Time Mode which is what they call a stationary antenna with high quality position information. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Fri, Mar 7, 2014 at 9:32 PM, Bob Camp li...@rtty.us wrote: On the 4's and 5's you only got a pulse + correction with the T model. I have a 6T so I can only read the data sheets for the others but the OP said uBlox-6. Perhaps there are various firmware releases but the LEA-5 family is described as being operationally the same as the LEA-6 family with respect to PG reports. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Didn't mean to cause a firestorm. Just used the term simple to describe a Lead/Lag D FF phase comparator. I view it as simple compared to a high speed counter. My GPSDO will have just such a FF whose state will be read by the micro which will implement a PI filter in software and drive a 20bit TI sigma delta DAC to apply corrections to the OCXO. Micro and all other clocks on the design are driven from the OCXO. I may switch the GPS module at a later date to one which provides sawtooth info if I really feel the need and add a delay line. Frankly I think I'll never get around to it. I'll publish a schematic, code and test results once I have something working. Thanks Jim ab3cv Date: Fri, 7 Mar 2014 09:23:54 -0800 From: Chris Albertson albertson.ch...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Another atomic clock question Message-ID: CABbxVHuc41UQMhgWNyCXdW=ichdg6taxeoka+zdv0hrrmo1...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 On Fri, Mar 7, 2014 at 5:25 AM, Jim Miller j...@jtmiller.com wrote: I think the hardware delay line approach is the only solution for a simple D FF lead/lag phase comparator. It would be placed ahead of the FF. Simple? You are going to need a micro controller and software to (1) tall the GPS to output the sawtooth function, they don't typically output it untell you tell it to. then (2) recover the sawtooth function from the serial data. Then(3) convert it to the counts that units used in the delay line. Finally (4) you need to interface the delay line to the processor and send the current sawtooth function value over that interface once per second. Also when I do stuff like this I always want some kind of LCD display or at least blink LEDS so I know what's going on inside and then it is at least running. Your simple analog devices no longer a simple analog device. Do a full up parts count for both designes. I think the digital correction comes in lower. Both solutions need the same micro controller and it's support circuitry. As to which GPSes send sawtooth. It's a common feature but typically you need to enable it, the same way you'd enable a self-survey or set a minimum elevation angle or whatever. Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 07/03/14 19:28, Lars Walenius wrote: Chris, about using one Arduino for two GPSDO controllers: Even if a microcontroller has lots of capacity I would recommend to use separate controllers for each oscillator. One of the reasons is what Tom van Baak said about using only one interrupt to avoid jitter and even if you trigger both channels from the same PPS and have just one interrupt you will have a problem that you can´t read two ADC´s at the same time. Even the HC390 I wouldn´t use for two different oscillators to prevent crosstalk. Both the processor and HC390 is so cheap it isn´t worth the risk IMO. Cross-talk typically happens though ground-bounce. Just using separate chips reduces the effect. May not be much of an issue at ns level, but below. Actually I would also recommend to put them in separate boxes even if it is more work (and I´m lazy ) to get best performance. Having two GPSDO´s that you can compare is very nice as long as you understand how they correlate , if that is not what you want to test. Of course you can also set one or both in hold mode to test them freerunning. Some telecom rubidiums have fairly noisy output. Steering an OCXO for clean-up might actually provide the best of both worlds. Holdover of the rubidiums and phase-noise of the OCXO. In that case, keeping them in the same box makes sense. The arduino could contribute long-term integrator memory and possibly do temperature compensation of the OCXO as a feed-forward approach. I have thought of connecting the M12 to the Arduino and if someone can help with code to get the sawtooth correction value into the Arduino and decoded I would be glad to have it. I've proposed to some of my local friends here, and we will probably do something with LPROs. We need to look at what GPS modules there is. I think sawtooth correction should be added. It's not that hard. One really wants two serial ports, one for the GPS and one for monitoring. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 08/03/14 00:52, Bob Camp wrote: Hi With a “real” 12 to 13 bit ADC and a 200 ns TDC pulse you would ideally get 200 / 4096 as your LSB. Nothing like this is ever perfect, so you probably aren’t going to get 50 ps. You probably will be below 100 ps. That’s plenty good enough to make sawtooth correction useful. When you have sawtooth corrections, the actual time of the PPS is not so important, but it will be that reference pulse which gives the high time-resolution info about the oscillators phase. The sawtooth correction will reduce the GPS modules TCXO into a common view oscillator which (almost) cancels out. If you do not have sawtooth corrections, indirect tracking might be possible to consider. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
j...@jtmiller.com said: I may switch the GPS module at a later date to one which provides sawtooth info if I really feel the need and add a delay line. Frankly I think I'll never get around to it. One nasty problem with hanging bridges is that if you don't believe in them, then you won't setup your monitoring system to notice them. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hello David, Not sure what is wrong here - I still can't reach it. If it isn't too much trouble - can you send me a screen shot off-list - I can look up the patents as long as the numbers are listed. Thanks! John W. Screen-shot and page HTML sent as requested. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
David, Thanks - got it. Best Regards, John W. On Fri, Mar 7, 2014 at 10:53 PM, David J Taylor david-tay...@blueyonder.co.uk wrote: Hello David, Not sure what is wrong here - I still can't reach it. If it isn't too much trouble - can you send me a screen shot off-list - I can look up the patents as long as the numbers are listed. Thanks! John W. Screen-shot and page HTML sent as requested. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
https://www.febo.com/pages/gps_pps/ It appears the implementation of the sawtooth error correction severely degrades the performance of the system. There could be many reasons, which is why it is important to nail down as many of the error sources as possible. severely degrades?? How do you reach this conclusion? It looks to me that sawtooth correction gives a 10x *improvement* in that plot. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Didier, If you intend to measure the 1PPS there is no need to correct or adjust it prior to measurement. Each second you simply apply the numerical sawtooth correction value to the numerical 1PPS measurement value. This is the pure software solution. Most people who use GPS for timing do it this way -- since they are already employing a sub-ns TIC to compare their standalone lab reference against the GPS tick. The software solution introduces no additional errors. This method also applies to any GPSDO which incorporates a digital TIC. On the other hand, if you intend to improve the accuracy of the 1PPS without measurement, you need a hardware solution instead. The classic approach is to delay, each second, the hardware 1PPS by N + sawtooth correction. You choose N (depends on the GPS receiver) so that the delay is never less than or too near zero. The one-chip solution I found was the Dallas DS1020 and that's what Rick used in his CNS-II product. Maxim (bought Dallas) now has alternative silicon delay lines that do the equivalent. Note the hardware solution is never quite as good as the software solution since there are offset, gain, linearity, and tempco issues with programmable delay lines. But it's usually close enough. Rick measured the difference between the two methods: 0.7 ns rms. See page 27-31 of http://www.cnssys.com/files/tow-time2009.pdf for details and his wonderful graphs. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi, Agree. If you steer so you keep to be off frequency so you have plenty of sawtooth you get better resolution. I've been pondering about maybe write an article to illustrate the effect. Cheers, Magnus On 04/03/14 23:45, Bob Camp wrote: Hi Be careful of what you wish for. One way to “eliminate” the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. The other way is to put the oscillator well off frequency. That way you have lots of sawtooth action. There are lots of ways to get an oscillator off frequency …. Bob On Mar 4, 2014, at 12:00 PM, Didier Juges shali...@gmail.com wrote: What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature. Didier KO4BB On March 3, 2014 6:51:54 PM CST, Charles Steinmetz csteinm...@yandex.com wrote: Chris wrote: If do have an external frequency reference then the crystal itself makes a good thermometer. So why not use THAT thermometer to control the heat added by the resister. Such a system would respond to changes in ambient temperature by adjusting the power in the resister. We don't even have to care if the crystal's temp-co is nonlinear because we are using a very small temperature range, so small it looks linear. I'll build it. Can you or anyone else subject a simple XCO schematic? Hopefully SIMPLE. What I need is a design that can be pulled down a few PPM so that I can raise it back with a bit of heat. I will have to be kept at a temperer above the hottest it will ever get inside the house, maybe 100F. See below or attached (hopefully). L and C are chosen to resonate at the crystal frequency with XC and XL in the general vicinity of 100 ohms to 1k ohms. What you are proposing is a disciplined oscillator using the oven setpoint as the control input. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi, You still get hanging bridges, but smaller in amplitude and for the same oscillator stability much more short-lived. Cheers, Magnus On 06/03/14 00:03, Bob Camp wrote: Hi If you are going to decode and use the sawtooth data out of the receiver, there’s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data…. Bob On Mar 5, 2014, at 9:53 AM, Mike M timen...@binsamp.e4ward.com wrote: Bob Camp wrote: Hi Be careful of what you wish for. One way to eliminate the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. Bob That's fine. Just set the oscillator to keep the bridge in the middle of the range. It should be possible to detect the correct frequency and phase by monitoring the sawtooth correction data from the GPS. Now you have eliminated the sawtooth error and no longer have to add correction for it. This will eliminate the quantization error in the sawtooth correction data since it is no longer needed. If the 1pps loop is properly designed, it should help the loop track the 1pps signal more accurately. Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
, modulating phase, frequency, voltage, temperature, etc. But as you spend too much time engineering this uncertain hack you maybe start to wonder if the real solution is just to apply known digital, numerical correction instead of wishful analog cover-up. Been there, done that. For more serious use, at the tens or unit nanosecond level, the robust solution is simply to apply 1PPS sawtooth correction from the receiver. The sawtooth error data is truncated at 1 ns. I would like to get far below that error. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. Tom, Thanks for your reply. The sawtooth error correction is described in Timing for VLBI, by Tom Clark and Rick Hambly, at http://www.cnssys.com/files/tow-time2011.pdf John Ackermann shows graphs that compare the results in GPS Pulse-per-Second Comparative Noise, at https://www.febo.com/pages/gps_pps/ It appears the implementation of the sawtooth error correction severely degrades the performance of the system. There could be many reasons, which is why it is important to nail down as many of the error sources as possible. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there?s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data?. Bob Thanks, Bob. I am not planning on heating the crystal. I want to replace it with a precision DDS. The sawtooth data is truncated at 1ns. I want to do much better. Again, this is not intended as a quick-and-dirty fix. I would like to separate out the error sources in a GPSDO and see what can be done to improve the results. Thanks, Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
, Tom Van Baak t...@leapsecond.com wrote: I agree with Bob. For casual use, hanging bridges are not really a problem, statistically speaking -- so don't worry. Yes, you can apply various techniques to reduce/eliminate the rare effect: forced temperature change, forced Vcc change, 2 or 3 or more shared-antenna receivers, modulating phase, frequency, voltage, temperature, etc. But as you spend too much time engineering this uncertain hack you maybe start to wonder if the real solution is just to apply known digital, numerical correction instead of wishful analog cover-up. Been there, done that. For more serious use, at the tens or unit nanosecond level, the robust solution is simply to apply 1PPS sawtooth correction from the receiver. The sawtooth error data is truncated at 1 ns. I would like to get far below that error. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. Tom, Thanks for your reply. The sawtooth error correction is described in Timing for VLBI, by Tom Clark and Rick Hambly, at http://www.cnssys.com/files/tow-time2011.pdf John Ackermann shows graphs that compare the results in GPS Pulse-per-Second Comparative Noise, at https://www.febo.com/pages/gps_pps/ It appears the implementation of the sawtooth error correction severely degrades the performance of the system. There could be many reasons, which is why it is important to nail down as many of the error sources as possible. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there?s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data?. Bob Thanks, Bob. I am not planning on heating the crystal. I want to replace it with a precision DDS. The sawtooth data is truncated at 1ns. I want to do much better. Again, this is not intended as a quick-and-dirty fix. I would like to separate out the error sources in a GPSDO and see what can be done to improve the results. Thanks, Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
To the Mike that posted: http://www.pst.netii.net/patents.htm - I tried going to your site - can't reach it. Is the site operational? I wanted to take a look at your patents. Thanks, John Westmoreland == Jon, It's working OK from Edinburgh at 07:08 UTC. David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Bob Camp wrote: Hi Be careful of what you wish for. One way to eliminate the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. Bob That's fine. Just set the oscillator to keep the bridge in the middle of the range. It should be possible to detect the correct frequency and phase by monitoring the sawtooth correction data from the GPS. Now you have eliminated the sawtooth error and no longer have to add correction for it. This will eliminate the quantization error in the sawtooth correction data since it is no longer needed. If the 1pps loop is properly designed, it should help the loop track the 1pps signal more accurately. Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi If you are going to decode and use the sawtooth data out of the receiver, there’s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data…. Bob On Mar 5, 2014, at 9:53 AM, Mike M timen...@binsamp.e4ward.com wrote: Bob Camp wrote: Hi Be careful of what you wish for. One way to eliminate the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. Bob That's fine. Just set the oscillator to keep the bridge in the middle of the range. It should be possible to detect the correct frequency and phase by monitoring the sawtooth correction data from the GPS. Now you have eliminated the sawtooth error and no longer have to add correction for it. This will eliminate the quantization error in the sawtooth correction data since it is no longer needed. If the 1pps loop is properly designed, it should help the loop track the 1pps signal more accurately. Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
I agree with Bob. For casual use, hanging bridges are not really a problem, statistically speaking -- so don't worry. Yes, you can apply various techniques to reduce/eliminate the rare effect: forced temperature change, forced Vcc change, 2 or 3 or more shared-antenna receivers, modulating phase, frequency, voltage, temperature, etc. But as you spend too much time engineering this uncertain hack you maybe start to wonder if the real solution is just to apply known digital, numerical correction instead of wishful analog cover-up. Been there, done that. For more serious use, at the tens or unit nanosecond level, the robust solution is simply to apply 1PPS sawtooth correction from the receiver. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there’s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data…. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi( While you see a lot of pretty plots in GPS spec sheets showing clean looking sawtooth sort of offsets marching down the page, that’s not what I see on a real receiver. The real data, even compared to a 5071A is much more random. It will indeed “hang”, but it also will reverse far more often than the pretty data sheets suggest. A simple model would be to add the sawtooth to some sort of random process. The sawtooth comes from the TCXO, the random looking stuff comes from the GPS solution. The oscillator in most timing modules is one form or another of a TCXO. Often they have digital compensation (one way or another). Their frequency versus temperature curves are not the simple third order curve you would expect from a bare crystal. They have a much higher order frequency versus temperature curve (6th, 8th …). That makes even the simple “frequency goes down when temp goes up” decision pretty tough. If they are doing some sort of auto correction TCXO based on the GPS it would get even more crazy. In that case the curve would be changing real time. Since the sawtooth changes multiple “runs” per minute in a room that holds 2C / 30 minutes, you could guess that a control of 0.01C would be needed to have any luck steering the oscillator. It’s nowhere near that simple, so that’s not even up to the “wild guess” level of confidence. If it’s close, that’s not going to be very easy all by it’s self. A double loop control is likely to be needed. Combine the random jitter with the (possibly) tough temperature control problem, and frequency reversals - this is a real can of worms. ——— Way lots easier approach: 1) You already need a CPU to set up the GPS, read the sawtooth data stream and do a control loop. It’s free / same with either approach. 2) Rip a VCTCXO out of something (or buy one cheap). 3) PWM control the TCXO, use it as your CPU clock 4) Generate a PPS with a timer output on the CPU. 5) Do a cheap / simple / easy TDC on the GPS pps, it will cost less that what ever was going to drive the heater. Now you have a GPSDO with a much lower jitter PPS output. You need to write from scratch code for the CPU either way. The code for the GPSDO is probably simpler than the temperature control code. It’s certainly no more difficult. This way you have an output at what ever the TCXO frequency is for “other stuff”. Bob On Mar 5, 2014, at 6:48 PM, Tom Van Baak t...@leapsecond.com wrote: I agree with Bob. For casual use, hanging bridges are not really a problem, statistically speaking -- so don't worry. Yes, you can apply various techniques to reduce/eliminate the rare effect: forced temperature change, forced Vcc change, 2 or 3 or more shared-antenna receivers, modulating phase, frequency, voltage, temperature, etc. But as you spend too much time engineering this uncertain hack you maybe start to wonder if the real solution is just to apply known digital, numerical correction instead of wishful analog cover-up. Been there, done that. For more serious use, at the tens or unit nanosecond level, the robust solution is simply to apply 1PPS sawtooth correction from the receiver. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there’s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data…. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? In the digital domain, 1nS resolution implies pretty fast clocks. On the other hand, processing a message that comes once per second to, say, drive a DAC is fairly trivial. Now, if we were to simply ignore the problem (an otherwise perfectly valid engineering choice under the right circumstances), we would not be time-nuts, would we? If you look at the number of posts on this list mentioning hanging bridges, it will show you that it is something most everyone has shown concern over at one time or another. I am still amazed at the simplicity and elegance of the Thunderbolt design where the issue of hanging bridges has been purely eliminated (not filtered, compensated, corrected or ignored) while making the design simpler and cheaper. It is much more robust than having to deal with a correction, no matter how well it is implemented. Now it is entirely possible that for most applications of interest to time-nuts, it is a negligible problem. I would not know but I defer to your qualified judgement. I have three Thunderbolts (the minimum number you have to have to resolve any discrepancy) and no other GPSDO, therefore I cannot comment on the relative merit of the two approaches from a practical standpoint. From a design standpoint, eliminating a problem by design (particularly when it is associated with a cost saving) is always preferable to an after the fact correction or compensation. Didier KO4BB On Wed, Mar 5, 2014 at 5:48 PM, Tom Van Baak t...@leapsecond.com wrote: I agree with Bob. For casual use, hanging bridges are not really a problem, statistically speaking -- so don't worry. Yes, you can apply various techniques to reduce/eliminate the rare effect: forced temperature change, forced Vcc change, 2 or 3 or more shared-antenna receivers, modulating phase, frequency, voltage, temperature, etc. But as you spend too much time engineering this uncertain hack you maybe start to wonder if the real solution is just to apply known digital, numerical correction instead of wishful analog cover-up. Been there, done that. For more serious use, at the tens or unit nanosecond level, the robust solution is simply to apply 1PPS sawtooth correction from the receiver. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there's no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Em 05/03/2014 22:43, Didier Juges escreveu: Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Using a DS1023 or a DS1124 plus a microcontroller to receive the RS232 message and program the chip to generate the desired delay: http://www.maximintegrated.com/datasheet/index.mvp/id/2608 http://www.maximintegrated.com/datasheet/index.mvp/id/5514 Daniel ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi The disconnect is that there is no need at all to correct for the delay with some sort of delay line setup. The sawtooth correction simply sums into the input of your control algorithm for the corrected oscillator. It’s nothing more than an adder that sums the TDC output with the sawtooth information. No delay lines, nothing fancy to it. You have everything you need in the CPU that reads the sawtooth data from the GPS module. The loop only gets an input once a second. You have *lots* of time for math. The output of the GPS module, if directly corrected for sawtooth still has a bunch of jitter on it. Even a disciplined TCXO will significantly improve things. Bob On Mar 5, 2014, at 8:43 PM, Didier Juges shali...@gmail.com wrote: Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? In the digital domain, 1nS resolution implies pretty fast clocks. On the other hand, processing a message that comes once per second to, say, drive a DAC is fairly trivial. Now, if we were to simply ignore the problem (an otherwise perfectly valid engineering choice under the right circumstances), we would not be time-nuts, would we? If you look at the number of posts on this list mentioning hanging bridges, it will show you that it is something most everyone has shown concern over at one time or another. I am still amazed at the simplicity and elegance of the Thunderbolt design where the issue of hanging bridges has been purely eliminated (not filtered, compensated, corrected or ignored) while making the design simpler and cheaper. It is much more robust than having to deal with a correction, no matter how well it is implemented. Now it is entirely possible that for most applications of interest to time-nuts, it is a negligible problem. I would not know but I defer to your qualified judgement. I have three Thunderbolts (the minimum number you have to have to resolve any discrepancy) and no other GPSDO, therefore I cannot comment on the relative merit of the two approaches from a practical standpoint. From a design standpoint, eliminating a problem by design (particularly when it is associated with a cost saving) is always preferable to an after the fact correction or compensation. Didier KO4BB On Wed, Mar 5, 2014 at 5:48 PM, Tom Van Baak t...@leapsecond.com wrote: I agree with Bob. For casual use, hanging bridges are not really a problem, statistically speaking -- so don't worry. Yes, you can apply various techniques to reduce/eliminate the rare effect: forced temperature change, forced Vcc change, 2 or 3 or more shared-antenna receivers, modulating phase, frequency, voltage, temperature, etc. But as you spend too much time engineering this uncertain hack you maybe start to wonder if the real solution is just to apply known digital, numerical correction instead of wishful analog cover-up. Been there, done that. For more serious use, at the tens or unit nanosecond level, the robust solution is simply to apply 1PPS sawtooth correction from the receiver. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there's no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi The sawtooth correction on a good GPS will go down to a few hundred ps over a thirty or so ns range. If you are going to correct, you need a chip that is accurate to 100 ps over a 30 ns ( 300 tap) range. That’s a tough part to find. Next you need to worry about jitter in the delay line …. Once you do all that, you still have a pretty messy PPS. Bob On Mar 5, 2014, at 9:02 PM, Daniel Mendes dmend...@gmail.com wrote: Em 05/03/2014 22:43, Didier Juges escreveu: Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Using a DS1023 or a DS1124 plus a microcontroller to receive the RS232 message and program the chip to generate the desired delay: http://www.maximintegrated.com/datasheet/index.mvp/id/2608 http://www.maximintegrated.com/datasheet/index.mvp/id/5514 Daniel ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Wed, Mar 5, 2014 at 5:43 PM, Didier Juges shali...@gmail.com wrote: Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Here is my plan for processing saw tooth data. If it's not going to work I'd rather hear about it now then a month from now after I've put in some effort. This is going into Lars' Arduino based GPSDO. Every second I read the voltage on a TIC capacitor. This tells by the phase in nanoseconds between the PPS and the OCXO. Then I add whatever the current GPS sawtooth value is to whatever my TIC said. I compare this to a set point. This is the phase error. The OCXO is adjusted based on a filtered version of this error. So in short, I don't correct even try to delay the pulse. I don't see any need to do that. I measure the pulse and get a number in nanoseconds. then I use sawtooth to correct the number. It seems way-hard and with no purpose to correct the pulse and then measure it. Better to correct the measurement. I think it is more accurate too a delay could never be perfect. The controller has LOT of spare capacity so I don't see way I can't add one of more TIC channels and a few more DACs I should be able to discipline an OCXO and my Rb oscillator from the same GPS PPS input. The 74HC360 is only 1/2 used an Arduino has enough spare pins. Any one more 74HC4046 and some passive parts would be required to build a dual channel GPSDO. It will be interesting to look at andompare the 10MHz outputs of two oscillators that are being disciplined by the same controller and GPS receiver. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Th On Wed, Mar 5, 2014 at 7:02 PM, Bob Camp li...@rtty.us wrote: Hi The disconnect is that there is no need at all to correct for the delay with some sort of delay line setup. The sawtooth correction simply sums into the input of your control algorithm for the corrected oscillator. It's nothing more than an adder that sums the TDC output with the sawtooth information. No delay lines, nothing fancy to it. Thanks this was exactly my plan, but I was wondering if I had missed something what others were talking about some really complex solutions. It works out to about one line of C code. Trivial, even on an 8-bit controller. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
is simply to apply 1PPS sawtooth correction from the receiver. The sawtooth error data is truncated at 1 ns. I would like to get far below that error. This issue comes up every now and then as people gradually transition from casual to serious use. I welcome any hard data or plots that demonstrate the difference among all approaches. There *is* a slight difference for sure. It's just that most people throw in the towel and use sawtooth corrections instead of trying to avoid them and cover up with less deterministic methods. Tom, Thanks for your reply. The sawtooth error correction is described in Timing for VLBI, by Tom Clark and Rick Hambly, at http://www.cnssys.com/files/tow-time2011.pdf John Ackermann shows graphs that compare the results in GPS Pulse-per-Second Comparative Noise, at https://www.febo.com/pages/gps_pps/ It appears the implementation of the sawtooth error correction severely degrades the performance of the system. There could be many reasons, which is why it is important to nail down as many of the error sources as possible. /tvb - Original Message - From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, March 05, 2014 3:03 PM Subject: Re: [time-nuts] Another atomic clock question Hi If you are going to decode and use the sawtooth data out of the receiver, there?s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data?. Bob Thanks, Bob. I am not planning on heating the crystal. I want to replace it with a precision DDS. The sawtooth data is truncated at 1ns. I want to do much better. Again, this is not intended as a quick-and-dirty fix. I would like to separate out the error sources in a GPSDO and see what can be done to improve the results. Thanks, Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature. Didier KO4BB On March 3, 2014 6:51:54 PM CST, Charles Steinmetz csteinm...@yandex.com wrote: Chris wrote: If do have an external frequency reference then the crystal itself makes a good thermometer. So why not use THAT thermometer to control the heat added by the resister. Such a system would respond to changes in ambient temperature by adjusting the power in the resister. We don't even have to care if the crystal's temp-co is nonlinear because we are using a very small temperature range, so small it looks linear. I'll build it. Can you or anyone else subject a simple XCO schematic? Hopefully SIMPLE. What I need is a design that can be pulled down a few PPM so that I can raise it back with a bit of heat. I will have to be kept at a temperer above the hottest it will ever get inside the house, maybe 100F. See below or attached (hopefully). L and C are chosen to resonate at the crystal frequency with XC and XL in the general vicinity of 100 ohms to 1k ohms. What you are proposing is a disciplined oscillator using the oven setpoint as the control input. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
I suggested yesterday to periodically heat and cool the oscillator, but my post may have been lost in the noise. Bob From: Didier Juges shali...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, March 4, 2014 11:00 AM Subject: Re: [time-nuts] Another atomic clock question What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature. Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hanging bridge? What is it; where is it found; and how does it form? My guess is that a Google or Wikipedia search is going to come up with something named Golden Gate or maybe a musical term. Tom Holmes, N8ZM -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Stewart Sent: Tuesday, March 04, 2014 12:08 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Another atomic clock question I suggested yesterday to periodically heat and cool the oscillator, but my post may have been lost in the noise. Bob From: Didier Juges shali...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, March 4, 2014 11:00 AM Subject: Re: [time-nuts] Another atomic clock question What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature. Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi Tom, You may have missed TVB's post yesterday, quoted below. A hanging bridge is an area on a timing receiver's plotted sawtooth correction value that stays on one side of phase zero for some period of time. As a result of this bias, a GPSDO that is not corrected for sawtooth will probably have at least a phase shift in its output frequency during a hanging bridge. It's not so bad on the newer 10ns receivers as it was on the older +/-52ns Oncores. If one could prevent these hanging bridges, an uncorrected GPSDO would likely track phase better. Tom suggested to detect when the bridge forms and give it a shot of heat. I suggested to vary the oscillator's frequency by periodically heating and cooling it. Tom's post: Sure. In fact you can loosely phase lock it to GPS that way. Your xtal doesn't need to have an EFC pin. You are using external temperature as a replacement for EFC. Call it TFC (temperature frequency control) instead. You can't get much simpler than that. Make sure to use a plain XO (not a TCXO or OCXO). I used a resistor heater to bust hanging-bridges: http://leapsecond.com/pages/vp/heater.htm /tvb From: Tom Holmes thol...@woh.rr.com To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Tuesday, March 4, 2014 12:07 PM Subject: Re: [time-nuts] Another atomic clock question Hanging bridge? What is it; where is it found; and how does it form? My guess is that a Google or Wikipedia search is going to come up with something named Golden Gate or maybe a musical term. Tom Holmes, N8ZM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
thol...@woh.rr.com said: Hanging bridge? What is it; where is it found; and how does it form? Tom Clark and Rick Hambly: Timing for VLBI http://gpstime.com/files/tow-time2009.pdf tvb: Motorola GPS M12+ Sawtooth http://www.leapsecond.com/pages/m12/sawtooth.htm -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Thanks Hal. Makes sense now. Just didn't have the right context in mind for the term. I see from tvb's paper that the Golden Gate result would have had a connection :-). Tom Holmes, N8ZM -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Tuesday, March 04, 2014 1:23 PM To: Discussion of precise time and frequency measurement Cc: hmur...@megapathdsl.net Subject: Re: [time-nuts] Another atomic clock question thol...@woh.rr.com said: Hanging bridge? What is it; where is it found; and how does it form? Tom Clark and Rick Hambly: Timing for VLBI http://gpstime.com/files/tow-time2009.pdf tvb: Motorola GPS M12+ Sawtooth http://www.leapsecond.com/pages/m12/sawtooth.htm -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi Be careful of what you wish for. One way to “eliminate” the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. The other way is to put the oscillator well off frequency. That way you have lots of sawtooth action. There are lots of ways to get an oscillator off frequency …. Bob On Mar 4, 2014, at 12:00 PM, Didier Juges shali...@gmail.com wrote: What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature. Didier KO4BB On March 3, 2014 6:51:54 PM CST, Charles Steinmetz csteinm...@yandex.com wrote: Chris wrote: If do have an external frequency reference then the crystal itself makes a good thermometer. So why not use THAT thermometer to control the heat added by the resister. Such a system would respond to changes in ambient temperature by adjusting the power in the resister. We don't even have to care if the crystal's temp-co is nonlinear because we are using a very small temperature range, so small it looks linear. I'll build it. Can you or anyone else subject a simple XCO schematic? Hopefully SIMPLE. What I need is a design that can be pulled down a few PPM so that I can raise it back with a bit of heat. I will have to be kept at a temperer above the hottest it will ever get inside the house, maybe 100F. See below or attached (hopefully). L and C are chosen to resonate at the crystal frequency with XC and XL in the general vicinity of 100 ohms to 1k ohms. What you are proposing is a disciplined oscillator using the oven setpoint as the control input. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi The simple approach is to use an op amp, a thermistor, and a couple of resistors. No need for anything digital. You can easily get all the gain possible (before oscillation) out of a very simple circuit. The net result will be about a 1C stability when you run it over temperature (say 0 to 50 C) in a lab chamber. You can tweak it a bit to get the thermal gain up to a few hundred if you have a chamber to give you feedback on your changes. Bob On Mar 3, 2014, at 5:18 AM, Hal Murray hmur...@megapathdsl.net wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 3/3/14 2:18 AM, Hal Murray wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. A number of microcontrollers have onchip temperature sensors (Freescale Kinetis, for instance). If the controller were bonded to the crystal housing, that might be enough coupling. Could you hold 0.1 or 0.001 degree? the chip has a 16 bid ADC, although I wouldn't trust the bottom bit or two because of noise. But in any case 1 LSB is 3.3/64k or about 50 microvolts. The temperature sensor slope is 1.715 mV/C, so that's in the 0.03 C/LSB range.. On a good day, you *might* be able to hold 0.1 degree, assuming there's no systematic errors. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hal, For science-fair level accuracy try a $2 PTC-60 thermistor heater one component oven for minimal complexity. I tried this with a small box and insulating foam and it gives surprisingly good results. Leave it to the ham radio guys to come up with a low cost solution. http://www.setileague.org/askdr/xtaloven.htm Richard Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi If you are measuring temperature in a room who’s temperature does not change, then yes you can hold 0.1 C. That of course is based on the “room does not change temperature” and that equates to absolutely no change at all. The only rational way to discus temperature stability is as a response to an external change. It change this amount when the temperature around it changes that amount. Trying to compare something on the table here and the table there is not a very useful exercise. On an OCXO the internal temperature control is always specified with a defined external temperature change. The drift in the set temperature at a constant ambient is essentially “un-measurable” even on some pretty cheap ovens. Bob On Mar 3, 2014, at 9:27 AM, Jim Lux jim...@earthlink.net wrote: On 3/3/14 2:18 AM, Hal Murray wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. A number of microcontrollers have onchip temperature sensors (Freescale Kinetis, for instance). If the controller were bonded to the crystal housing, that might be enough coupling. Could you hold 0.1 or 0.001 degree? the chip has a 16 bid ADC, although I wouldn't trust the bottom bit or two because of noise. But in any case 1 LSB is 3.3/64k or about 50 microvolts. The temperature sensor slope is 1.715 mV/C, so that's in the 0.03 C/LSB range.. On a good day, you *might* be able to hold 0.1 degree, assuming there's no systematic errors. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Mon, Mar 3, 2014 at 2:18 AM, Hal Murray hmur...@megapathdsl.net wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. There is only one value of perfect. The goal is to keep the frequency spot-on the marked 10MHz If this system works the crystal never moves off it's design value. We are not using het to push or pull the crystal off it's fundamental design point but maybe we say to push or pull it back to center. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. That is my goal too. I'm never impressed that people with unlimited budget do good work. But doing the same with recycled junk parts really is impressive. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. Why are you measuring temperature. Just let it be whatever. You measure the frequent and then adult the current in the heater to keep the frequency constant. I assume that if the crystal really is a good thermometer then frequency is all you need to measure. One can make the control easier by adding some thermal mass. A big chunk of metal would add some stability. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
In message ab202da8-82bd-4861-af15-abbf92779...@rtty.us, Bob Camp writes: If you are measuring temperature in a room who's temperature does not change, then yes you can hold 0.1 C. That would make you quite famous, since the current best measurement of Bolzmans constant has a relative uncertainty of 0.71e-6. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
The OCXO maker is forced to use a temperature sensor because he does not have access to a frequency reference. If do have an external frequency reference then the crystal itself makes a good thermometer. So why not use THAT thermometer to control the heat added by the resister.Such a system would respond to changes in ambient temperature by adjusting the power in the resister. We don't even have to care if the crystal's temp-co is nonlinear because we are using a very small temperature range, so small it looks linear. I'll build it.Can you or anyone else subject a simple XCO schematic? Hopefully SIMPLE. What I need is a design that can be pulled down a few PPM so that I can raise it back with a bit of heat. I will have to be kept at a temperer above the hottest it will ever get inside the house, maybe 100F. On Mon, Mar 3, 2014 at 3:18 PM, Bob Camp li...@rtty.us wrote: Hi If you are measuring temperature in a room who's temperature does not change, then yes you can hold 0.1 C. That of course is based on the room does not change temperature and that equates to absolutely no change at all. The only rational way to discus temperature stability is as a response to an external change. It change this amount when the temperature around it changes that amount. Trying to compare something on the table here and the table there is not a very useful exercise. On an OCXO the internal temperature control is always specified with a defined external temperature change. The drift in the set temperature at a constant ambient is essentially un-measurable even on some pretty cheap ovens. Bob On Mar 3, 2014, at 9:27 AM, Jim Lux jim...@earthlink.net wrote: On 3/3/14 2:18 AM, Hal Murray wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. A number of microcontrollers have onchip temperature sensors (Freescale Kinetis, for instance). If the controller were bonded to the crystal housing, that might be enough coupling. Could you hold 0.1 or 0.001 degree? the chip has a 16 bid ADC, although I wouldn't trust the bottom bit or two because of noise. But in any case 1 LSB is 3.3/64k or about 50 microvolts. The temperature sensor slope is 1.715 mV/C, so that's in the 0.03 C/LSB range.. On a good day, you *might* be able to hold 0.1 degree, assuming there's no systematic errors. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi The crystal as normally cut makes a very poor thermometer compared to a thermistor. Bob On Mar 3, 2014, at 6:46 PM, Chris Albertson albertson.ch...@gmail.com wrote: The OCXO maker is forced to use a temperature sensor because he does not have access to a frequency reference. If do have an external frequency reference then the crystal itself makes a good thermometer. So why not use THAT thermometer to control the heat added by the resister.Such a system would respond to changes in ambient temperature by adjusting the power in the resister. We don't even have to care if the crystal's temp-co is nonlinear because we are using a very small temperature range, so small it looks linear. I'll build it.Can you or anyone else subject a simple XCO schematic? Hopefully SIMPLE. What I need is a design that can be pulled down a few PPM so that I can raise it back with a bit of heat. I will have to be kept at a temperer above the hottest it will ever get inside the house, maybe 100F. On Mon, Mar 3, 2014 at 3:18 PM, Bob Camp li...@rtty.us wrote: Hi If you are measuring temperature in a room who's temperature does not change, then yes you can hold 0.1 C. That of course is based on the room does not change temperature and that equates to absolutely no change at all. The only rational way to discus temperature stability is as a response to an external change. It change this amount when the temperature around it changes that amount. Trying to compare something on the table here and the table there is not a very useful exercise. On an OCXO the internal temperature control is always specified with a defined external temperature change. The drift in the set temperature at a constant ambient is essentially un-measurable even on some pretty cheap ovens. Bob On Mar 3, 2014, at 9:27 AM, Jim Lux jim...@earthlink.net wrote: On 3/3/14 2:18 AM, Hal Murray wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C albertson.ch...@gmail.com said: So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure, for some values of perfect and such. I've occasionally thought about building something like this, just for the hell of it to see what happens and/or what I learn, and or how good I/we can get on a low budget. I think there are two problem areas. One is sensors and control algorithms. The other is board layout. Where is the sweet spot on complexity vs accuracy? I'm looking for science-fair level of goodness rather than super-expensive to get another 0 or two. What's the best low-cost way to measure temperature? Many of the obvious choices are only good to 0.1 C. That's great if you are trying to measure room temperature or or want to keep your CPU from melting, but it's probably leaving a lot on the table if you are interested in the frequency from a crystal. My straw man would be a thermistor and OP-Amp feeding into the ADC on your favorite uProc. Maybe the other side of a bridge would be adjustable. A number of microcontrollers have onchip temperature sensors (Freescale Kinetis, for instance). If the controller were bonded to the crystal housing, that might be enough coupling. Could you hold 0.1 or 0.001 degree? the chip has a 16 bid ADC, although I wouldn't trust the bottom bit or two because of noise. But in any case 1 LSB is 3.3/64k or about 50 microvolts. The temperature sensor slope is 1.715 mV/C, so that's in the 0.03 C/LSB range.. On a good day, you *might* be able to hold 0.1 degree, assuming there's no systematic errors. How much power do you need to keep things warm? I'm assuming something like a watt or 2 with something like a PWM from the uProc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Sure. In fact you can loosely phase lock it to GPS that way. Your xtal doesn't need to have an EFC pin. You are using external temperature as a replacement for EFC. Call it TFC (temperature frequency control) instead. You can't get much simpler than that. Make sure to use a plain XO (not a TCXO or OCXO). I used a resistor heater to bust hanging-bridges: http://leapsecond.com/pages/vp/heater.htm /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Tom, That's a pretty interesting idea. It makes me wonder if it would be worth it to switch perhaps a 1/2W heat source (random number) off and on over the XO in the UT+ say every minute or so. Bob From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, March 3, 2014 6:40 PM Subject: Re: [time-nuts] Another atomic clock question Sure. In fact you can loosely phase lock it to GPS that way. Your xtal doesn't need to have an EFC pin. You are using external temperature as a replacement for EFC. Call it TFC (temperature frequency control) instead. You can't get much simpler than that. Make sure to use a plain XO (not a TCXO or OCXO). I used a resistor heater to bust hanging-bridges: http://leapsecond.com/pages/vp/heater.htm /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Mon, Mar 3, 2014 at 4:51 PM, Charles Steinmetz csteinm...@yandex.com wrote: What you are proposing is a disciplined oscillator using the oven setpoint as the control input. What I want to try is building a GPSDO for say $25 for everything except the GPS. A fun contest would be to adopt some low budget, like $20 and see who can make the best ADEV numbers. A rules would have to be only fair market prices for components, not fair if you buys $1 rubidium clock. It would have to be prices that anyone could get any day. Or you fix the task and lowest priced design wins. Say the test is a lab 10MHz reference good to 11 digits then see who can do the job at lowest cost. Thanks that schematic looks to be the exact one I was looking for, I've got most of the rest of what's needed to connect it to a GPS. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi So I can use the scrap (zero value) 5 MHz 3rd OT HC-40 package SC’s that are sitting in a pile in the basement right ? Bob On Mar 3, 2014, at 8:47 PM, Chris Albertson albertson.ch...@gmail.com wrote: On Mon, Mar 3, 2014 at 4:51 PM, Charles Steinmetz csteinm...@yandex.com wrote: What you are proposing is a disciplined oscillator using the oven setpoint as the control input. What I want to try is building a GPSDO for say $25 for everything except the GPS. A fun contest would be to adopt some low budget, like $20 and see who can make the best ADEV numbers. A rules would have to be only fair market prices for components, not fair if you buys $1 rubidium clock. It would have to be prices that anyone could get any day. Or you fix the task and lowest priced design wins. Say the test is a lab 10MHz reference good to 11 digits then see who can do the job at lowest cost. Thanks that schematic looks to be the exact one I was looking for, I've got most of the rest of what's needed to connect it to a GPS. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Yes, there is some satisfaction is measuring to fine tolerances. Of all the physical measurements we can take, frequency can be measured with the most accuracy.You say 1ppb is enough.Let's see a billion is 1E9. A 10Mhz signal is 1E7 cycles per second 9-7 is 2. You can get to 1ppm simplify counting cycles for 100 seconds or less than 2 minutes. Had you needed 1E-12 level then 7-12 is five which means 100,000 seconds or about 30 hours. So you get your answer in some amount of time but likely it takes several measurement cycles to converge and you oscillator must be good enough to be stable over that long of a period. You can speed up the convergence by a lot if you compare clocks using a finer measure than full cycles, You can measrure small fractions of cycles (phase) and then make an adjustment every second. My opinion: For 1ppm you will need any reasonable GPS receiver that has a 1PPS output. You can find them that are really good and put the pulse out within single digit nanoseconds of the correct time but you can use a GPS that gets to 100ns or even a few hundred ns. An older Motorola encore sells for about $20 on eBay. Then you need antenna and power supply. The guys who are going for the last ns will buy a better GPS, place the antenna on a tall mast on the roof, measure all their cables and look for an ultra clean power supply. You don't need any of that. Look for the thread here on this list about the Arduino based GPSDO. I think this will be the most economical one ever. I'm thinking under $50. and that include a $25 ovenized crystal oscillator from eBay. Five years ago people would tell youth just buy a Thunderbolt but prices have gone up 3X on those. Maybe that was a good thing, now peole will have to think a little harder. On Sat, Mar 1, 2014 at 10:48 PM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use numbers. Say and be able to adjust them at the 1E-8 level. Then you will get advice to just use WWV. But what if you need 10,000 times better? Then use GPS After that it starts getting harder but you still are not up to as well as they can be. I admit to a few years ago using a 50 cent TTL can oscillator as my lab standard The part was salvage from some junk and was good to about 5 digits accuracy. It worked actually better than I needed. My RF signal generator was from the 1960's with a hand turned dial to adjust the frequency. The TTL can let me calibrate the dial. I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency. I did WWV at 20 MHz for a beat of somewhat slower than one per second. I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly. And I don't need phase lock to them anyway. In the old days they had 25 MHz and even 30 MHz for a slight improvement in settability if not stability. Bob On Saturday, March 1, 2014 7:38 PM, Hal Murray hmur...@megapathdsl.net wrote: I am trying to understand how this is done. Should I ever get a rubidium standard, I'd want to check its calibration, and that's not a trivial exercise. If you assume your rubidium is stable, then it's pretty easy to check and/or calibrate. The trick is that you need someplace to stand. A PC running ntp is good long term. There is a tradeoff between good and long. Good is ambiguous, but both how-good is your PC clock and how good/accurate a measurement do you
Re: [time-nuts] Another atomic clock question
In a message dated 02/03/2014 02:07:05 GMT Standard Time, bob91...@yahoo.com writes: All this is very interesting. However, my interest is frequency. In other words, I want to know that my standard oscillators are as close to desired frequency as possible, and how close that turns out to be. - Hi Bob Without wanting to get bogged down in questions of how long is a piece of string and close is close etc etc, I do think your best starting point would be a GPS frequency standard. Nothing is ever perfect, but without reliable access to alternatives, such as Loran or WWVB and its equivalents, a GPSDO is still just about the only option available at anywhere near a sensible price that is likely to do what you're asking. It shouldn't mean either that buying one automatically excludes the option of eventually building your own, or otherwise getting more deeply involved. Once started on the slippery slope there's more than enough opportunity for experimentation with well proven designs and concepts aready out there to provide endless fun, and/or frustration:-) After that there's no telling where you might end up:-) It is true, as has been stated, that the Trimble Thunderbolt isn't quite the economic entry point it once was, but that doesn't mean there aren't viable alternatives. One good example is the Trimble Nortel NTGS50AA, as can be found in Ebay buy it now 291054324150 and often for a bit less in auctions from the same seller. These might be getting a bit long in the tooth, there has been some experience of oscillator's having aged to outside the unit's EFC range, although they generally do work out of the box, even though there isn't one:-), but the seller is helpful and should it prove necessary the oscillator can be changed with a bit of care. As a bonus, Lady Heather, she of Thunderbolt whipping fame, can also knock these into shape, and there's plenty of existing users here with experience of them. There is then, of course, the consideration of how you compare your oscillators with the standard, do you have or do you invest in an appropriate frequency counter?, do you have or do you invest in a suitable 'scope plus the necessary time to monitor the drift?, and so on and so fifth. What was that about the length of a piece of string?:-) Regards Nigel GM8PZR Yes, the Internet gives me time of day as close as I care to know. I have an 'atomic' clock from LaCrosse that resets itself nightly, although it's fussy about where in the house I put it. If I put it where I'd like, it won't receive WWVB, so I put it across the room. I called the company inquiring about augmenting the internal antenna but they were of no help. While watching the clock and listening to WWV, it seems the clock is a fraction of a second behind. Even that doesn't matter, but calibrating the counter time base is another kind of thing. I am trying to understand how this is done. Should I ever get a rubidium standard, I'd want to check its calibration, and that's not a trivial exercise. Bob On Saturday, March 1, 2014 4:56 PM, Paul Alfille paul.alfi...@gmail.com wrote: There are WWVB clocks with serial output. Arcron made one that I added linux ntp support for some years back. http://www.atomictimeclock.com/radsynarcron.htm http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver27.html As I recall, it was under $100, quite nicely styled, and is sitting here on my desk. (Reception on the East Coast can be spotty, so I've switched to standard internet net time source). On Mon, Feb 24, 2014 at 7:44 AM, Bob Camp li...@rtty.us wrote: Hi Ok, so 0.1 second at the sync point is indeed a reasonable estimate. If that's all you need to deal with (you correct out the crystal offset one way or the other) then: At 1 day you have 11.5 ppm accuracy. Roughly a 100 Hz beat note with WWV at 10 MHz. At 10 days you have 1.15 ppm. Roughly a 1 Hz beat note at 10 MHz. At 100 days you have 0.115 ppm. That would be about a 10 second period beat note. None of that is to say that a beat note is all there is to getting accuracy off of WWV or that the two approaches deliver the same net accuracy. Yes I've done the 10 second beat thing, it can be done with care and a good stable WWV signal. Bob On Feb 23, 2014, at 5:21 PM, Tom Van Baak t...@leapsecond.com wrote: Now that you have brought up this subject, do you know of any way to use these LaCrosse clocks to calibrate frequency standards? I suggest using a direct electric (1.5 VDC high-Z) or indirect magnetic (high gain) pickup on the coil to get the +/- pulse per second. Compare this time with your local frequency standard and over several days you should get accuracy better than 10 ms per day (1e-7). Here's an example of a raw phase plot: http://leapsecond.com/pages/Junghans/
Re: [time-nuts] Another atomic clock question
My opinion: For 1ppm you will need any reasonable GPS receiver that has a 1PPS output. You can find them that are really good and put the Chris, I agree investing in a cheap GPS receiver is a good step for anyone playing with time frequency. I would recommend the same. But I'd like to point out that 1 ppm is an easy goal and you don't need GPS for that. For example, a 10811A OCXO has a frequency drift spec of 5e-10/day and 1e-7/year. We know that after continuous use most 10811 are far better than this. Even the manual mentions typical 1e-8 / year after 1 year. So that means if you buy a 10811, it should stay within 1 ppm -- for your rest of your life. No GPS. No antenna. No worries. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi When you say “adjust crystals close” do you mean: 1) Grinding / plating crystal blanks? (as in fabricating crystals from scratch) 2) Setting uncompensated crystal oscillators on frequency? (as in some radios) 3) Calibrating the OCXO that is the master reference for an instrument? That all covers a lot of ground. Cost wise, there isn’t much price difference between an Rb and a GPSDO. Both are overkill for numbers 1 and 2, but they are what is commonly used in industry. For number 3 it’s a “that depends”. Some instruments have much better OCXO’s in them than others. The GPSDO with it’s self calibrating capability is often the device chosen for 3. Bob On Mar 1, 2014, at 11:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency. I did WWV at 20 MHz for a beat of somewhat slower than one per second. I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly. And I don't need phase lock to them anyway. In the old days they had 25 MHz and even 30 MHz for a slight improvement in settability if not stability. Bob On Saturday, March 1, 2014 7:38 PM, Hal Murray hmur...@megapathdsl.net wrote: I am trying to understand how this is done. Should I ever get a rubidium standard, I'd want to check its calibration, and that's not a trivial exercise. If you assume your rubidium is stable, then it's pretty easy to check and/or calibrate. The trick is that you need someplace to stand. A PC running ntp is good long term. There is a tradeoff between good and long. Good is ambiguous, but both how-good is your PC clock and how good/accurate a measurement do you want are appropriate. Probably the simplest way is to get one of tvb's preprogrammed PICs. http://www.leapsecond.com/pic/picdiv.htm http://www.leapsecond.com/pic/picpet.htm One approach is to use a picDIV to make a PPS and then monitor that. If you have Linux, you can feed the PPS to a serial port. My hack for counting 60Hz will work fine at 1 Hz. http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz.py Another approach is to use a picPET and connect a modem control signal from the monitoring PC to the Event input on the picPET. Then the data collection program grabs the time, flaps a modem control signal, grabs the time again, then grabs the text from the picPET and logs everything. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi Assuming you are after a reference at 10 ppb accuracy: 10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use numbers. Say and be able to adjust them at the 1E-8 level. Then you will get advice to just use WWV. But what if you need 10,000 times better? Then use GPS After that it starts getting harder but you still are not up to as well as they can be. I admit to a few years ago using a 50 cent TTL can oscillator as my lab standard The part was salvage from some junk and was good to about 5 digits accuracy. It worked actually better than I needed. My RF signal generator was from the 1960's with a hand turned dial to adjust the frequency. The TTL can let me calibrate the dial. I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency. I did WWV at 20 MHz for a beat of somewhat slower than one per second. I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly. And I don't need phase lock to them anyway. In the old days they had 25 MHz and even 30 MHz for a slight improvement in settability if not stability. Bob On Saturday, March 1, 2014 7:38 PM, Hal Murray hmur...@megapathdsl.net wrote: I am trying to understand how this is done. Should I ever get a rubidium standard, I'd want to check its calibration, and that's not a trivial exercise. If you assume your rubidium is stable, then it's pretty easy to check and/or calibrate. The trick is that you need someplace to stand. A PC running ntp is good long term. There is a tradeoff between good and long. Good is ambiguous, but both how-good is your PC clock and how good/accurate a measurement do you want are appropriate. Probably the simplest way is to get one of tvb's preprogrammed PICs. http://www.leapsecond.com/pic/picdiv.htm http://www.leapsecond.com/pic/picpet.htm One approach is to use a picDIV to make a PPS and then monitor that. If you have Linux, you can feed the PPS to a serial port. My hack for counting 60Hz will work fine at 1 Hz.
Re: [time-nuts] Another atomic clock question
I'm not ready to delve into temperature measurement. But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Again, how does one calibrate those 3 MHz ovenized units? Bob On Sunday, March 2, 2014 7:41 AM, Bob Camp li...@rtty.us wrote: Hi Assuming you are after a reference at 10 ppb accuracy: 10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use numbers. Say and be able to adjust them at the 1E-8 level. Then you will get advice to just use WWV. But what if you need 10,000 times better? Then use GPS After that it starts getting harder but you still are not up to as well as they can be. I admit to a few years ago using a 50 cent TTL can oscillator as my lab standard The part was salvage from some junk and was good to about 5 digits accuracy. It worked actually better than I needed. My RF signal generator was from the 1960's with a hand turned dial to adjust the frequency. The TTL can let me calibrate the dial. I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency. I did WWV at 20 MHz for a beat of somewhat slower than one per second. I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly. And I don't need phase lock to them anyway. In the old days they had 25 MHz and even 30 MHz for a slight improvement in settability if not stability. Bob On Saturday, March 1, 2014 7:38 PM, Hal Murray hmur...@megapathdsl.net wrote: I am trying to understand how this is done. Should I ever get a rubidium standard, I'd want to check its calibration, and that's not a trivial exercise. If you assume your rubidium is stable, then it's pretty easy to check and/or calibrate. The trick is that you need someplace to stand. A PC running ntp is good long term. There is a tradeoff between good and long. Good is ambiguous, but both how-good is your PC clock and how good/accurate a
Re: [time-nuts] Another atomic clock question
Yes Nigel, it's a waste of time but so are computer games and going to Disneyland and such. We do it because we get pleasure, and nobody can criticize that. I am a bit confused over your mention of Trimble units. I'm not familiar with them or what they are supposed to do. I better do some homework. I know if I use an X-Y 'scope with two reasonably clean signals I can adjust one for a stable pattern and so, depending on how long it holds still, know how close the two frequencies are. I can get one signal from my counter time base, but where do I get the standard signal? Bob On , Bob Albert bob91...@yahoo.com wrote: I'm not ready to delve into temperature measurement. But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Again, how does one calibrate those 3 MHz ovenized units? Bob On Sunday, March 2, 2014 7:41 AM, Bob Camp li...@rtty.us wrote: Hi Assuming you are after a reference at 10 ppb accuracy: 10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use numbers. Say and be able to adjust them at the 1E-8 level. Then you will get advice to just use WWV. But what if you need 10,000 times better? Then use GPS After that it starts getting harder but you still are not up to as well as they can be. I admit to a few years ago using a 50 cent TTL can oscillator as my lab standard The part was salvage from some junk and was good to about 5 digits accuracy. It worked actually better than I needed. My RF signal generator was from the 1960's with a hand turned dial to adjust the frequency. The TTL can let me calibrate the dial. I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency. I did WWV at 20 MHz for a beat of somewhat slower than one per second. I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly. And I don't need phase lock to them anyway. In the old days they had 25
Re: [time-nuts] Another atomic clock question
Hi On Mar 2, 2014, at 10:58 AM, Bob Albert bob91...@yahoo.com wrote: I'm not ready to delve into temperature measurement. But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Again, how does one calibrate those 3 MHz ovenized units? Bob Depending on their age and intended use, the crystal in an OCXO could be an AT, a BT, an X-cut, or an SC. In all cases the adjustment process is similar. The oven temperature is adjusted for minimum (or maximum) frequency to put it on the “turn” of the crystal. Then the unit is put in a test chamber and run over temperature. Based on the data, the oven temp is adjusted to zero out the temperature effects of the whole circuit. If absolute best temperature performance is not required, the temp run step may be left out. On Sunday, March 2, 2014 7:41 AM, Bob Camp li...@rtty.us wrote: Hi Assuming you are after a reference at 10 ppb accuracy: 10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use numbers. Say and be able to adjust them at the 1E-8 level. Then you will get advice to just use WWV. But what if you need 10,000 times better? Then use GPS After that it starts getting harder but you still are not up to as well as they can be. I admit to a few years ago using a 50 cent TTL can oscillator as my lab standard The part was salvage from some junk and was good to about 5 digits accuracy. It worked actually better than I needed. My RF signal generator was from the 1960's with a hand turned dial to adjust the frequency. The TTL can let me calibrate the dial. I probably will never go rubidium (note that I qualified that) but still somewhere one has to decide where to set the frequency. I did WWV at 20 MHz for a beat of somewhat slower than one per second. I know the phase changes but probably not much in a few minutes, as the path length doesn't vary very quickly. And I don't need
Re: [time-nuts] Another atomic clock question
Hi Trimble is one of many companies in the GPSDO business. A GPSDO is an oscillator that is locked up to the GPS signal. In many cases the oscillator is a pretty good OCXO. Trimble made a lot of these for the cell tower people. They now show up pretty regularly on the surplus market. A GPSDO from just about anybody will give you a very good local reference. They cost $100 to $20,000 depending on where you get them and how hard you shop. I would suggest one at the lower end of that range for what you are trying to do :). A number of them have sold recently on eBay for about $130. Most GPSDO’s will put out 10 MHz. Plug that into your counter / synthesizer / radio / service monitor and it’s as accurate as the GPSDO. Doing a frequency check is now as simple as running your test gear. No added steps no messing around. Bob On Mar 2, 2014, at 11:03 AM, Bob Albert bob91...@yahoo.com wrote: Yes Nigel, it's a waste of time but so are computer games and going to Disneyland and such. We do it because we get pleasure, and nobody can criticize that. I am a bit confused over your mention of Trimble units. I'm not familiar with them or what they are supposed to do. I better do some homework. I know if I use an X-Y 'scope with two reasonably clean signals I can adjust one for a stable pattern and so, depending on how long it holds still, know how close the two frequencies are. I can get one signal from my counter time base, but where do I get the standard signal? Bob On , Bob Albert bob91...@yahoo.com wrote: I'm not ready to delve into temperature measurement. But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Again, how does one calibrate those 3 MHz ovenized units? Bob On Sunday, March 2, 2014 7:41 AM, Bob Camp li...@rtty.us wrote: Hi Assuming you are after a reference at 10 ppb accuracy: 10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use
Re: [time-nuts] Another atomic clock question
BA I am a bit confused over your mention of Trimble units. I'm not familiar with them or what they are supposed to do. BA I better do some homework. The best thing said so far ... Scan the archives and Google for GPSDO, do some research and reading Then the archives for Trimble then for Thunderbolt If you Google for the two word Trimble and Thunderbolt it should give you a good 2-3 hours of reading from the over 100,000 hits. On Sun, Mar 2, 2014 at 8:03 AM, Bob Albert bob91...@yahoo.com wrote: Yes Nigel, it's a waste of time but so are computer games and going to Disneyland and such. We do it because we get pleasure, and nobody can criticize that. I am a bit confused over your mention of Trimble units. I'm not familiar with them or what they are supposed to do. I better do some homework. I know if I use an X-Y 'scope with two reasonably clean signals I can adjust one for a stable pattern and so, depending on how long it holds still, know how close the two frequencies are. I can get one signal from my counter time base, but where do I get the standard signal? Bob On , Bob Albert bob91...@yahoo.com wrote: I'm not ready to delve into temperature measurement. But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Again, how does one calibrate those 3 MHz ovenized units? Bob On Sunday, March 2, 2014 7:41 AM, Bob Camp li...@rtty.us wrote: Hi Assuming you are after a reference at 10 ppb accuracy: 10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert bob91...@yahoo.com wrote: Chris, Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. My need for this is nonexistent. I am only interested in doing it for the fun of seeing all zeros on the counter and having it give me that repeatedly. The pleasure of knowing I am as close as the equipment is capable is what I seek. I'm sure many time nuts feel the same. I am not interested in offering a calibration service or tracking spacecraft or measuring the diameter of the moon. How do I get accurate frequency from GPS? I have the same fetish regarding components, resistors and capacitors and inductors. I have lots of good meters but am always looking for a better one. I am trying to get six useful digits of voltage and resistance measurement and eventually want to do it with current as well. Not so sure about temperature, mass, and force. Once I get where I want to be, I'll probably go into basket weaving. Bob On Sunday, March 2, 2014 5:46 AM, Chris Albertson albertson.ch...@gmail.com wrote: On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert bob91...@yahoo.com wrote: Paul, as I said I just want to know how close my crystals are and be able to adjust them as well as they can be. Don't say as well as can be that can get expensive and time consuming. You need to use numbers. Say and be able to adjust them at the 1E-8 level. Then you will get advice to just use WWV. But what if you need 10,000 times better? Then use GPS After that it starts getting harder but you still are not up to as well as they can be. I admit to a few years ago using a 50 cent TTL can oscillator as my lab standard The part was salvage from some junk and was good to about 5 digits accuracy. It worked actually better than I needed. My
Re: [time-nuts] Another atomic clock question
li...@rtty.us said: A number of them have sold recently on eBay for about $130. Don't forget the antenna and power supply. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
In a message dated 02/03/2014 16:06:49 GMT Standard Time, bob91...@yahoo.com writes: Yes Nigel, it's a waste of time but so are computer games and going to Disneyland and such. We do it because we get pleasure, and nobody can criticize that. - Hi Bob, I'm not sure where the waste of time comes in, that's certainly not something I was suggesting, although perhaps not quite so convinced when it comes to computer games and/or Disneyland:-) It might become time consuming, even to the point of becoming an obsession, but that still doesn't stop it being a very rewarding obsession:-) I'm sorry, I had assumed you would at least be somewhat familiar with what I was referring to. Trimble made a GPS disciplined oscillator called the Thunderbolt, that was a reference to a comment in a previous reply, available on the surplus market but now more expensive than they used to be. The other unit I mentioned was what I considered to be a reasonably priced alternative. Trimble are just one manufacturer of such items, it's also possible to build your own, so some searches on GSP disciplined or conditioned oscillators, GPSDOs for short, might indeed be very worthwhile. Basically, what they do is correct the drift of a local oscillator, usually contained within that unit and often 10MHz but not necessarily so, against the frequency references used by the GPS satellites, and this gives you your standard signal, so as well as the unit itself you need a GPS antenna to receive the satellite signals. There's a variety of factors that will affect resolution and stability but 1 part ber billion should be straightforward plug 'n go, and I would expect a few parts in 10^10 with very little effort. Because of the way this works the GPS reference itself doesn't need any additional calibration, so if you did eventually decide to go for a rubidium oscillator, as you suggested you might, this could be one way of calibrating that. Regards Nigel GM8PZR I am a bit confused over your mention of Trimble units. I'm not familiar with them or what they are supposed to do. I better do some homework. I know if I use an X-Y 'scope with two reasonably clean signals I can adjust one for a stable pattern and so, depending on how long it holds still, know how close the two frequencies are. I can get one signal from my counter time base, but where do I get the standard signal? Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
bob91...@yahoo.com said: But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Most crystals are low cost. They will have a temperature characteristic similar to the graph about half way down this URL: http://www.4timing.com/techcrystal.htm The specs on the standard oscillator packages vary from 100ppm to 20ppm. That covers temperature and voltage and initial manufacturing and some amount of aging. (I haven't looked at the spec sheets recently. I don't remember seeing anything about aging.) The point is that they are low cost and the specs are reasonably clear, something a digital designer can understand and use. Again, how does one calibrate those 3 MHz ovenized units? I plug mine into a HP 5334B which is clocked by a TBolt. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi Depending on which auction you find and what they include you may indeed have some other bits and pieces to dig up as well. The prices run in cycles, so you will always pay a bit more if you “want it right now” than if you are willing to sit back and shop for a few months. Bob On Mar 2, 2014, at 12:13 PM, Hal Murray hmur...@megapathdsl.net wrote: li...@rtty.us said: A number of them have sold recently on eBay for about $130. Don't forget the antenna and power supply. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi These days, you can get some *very* low cost crystals. They sell by the pound rather than by the piece. The tolerance as delivered may be 0.1% for temperature plus calibration. Aging is likely to be “who knows”. The temperature characteristic could be a third order curve. More likely it’s a straight line in one direction or the other. Cost is the driver, and not much else matters. They make millions of them a week. Bob On Mar 2, 2014, at 12:56 PM, Hal Murray hmur...@megapathdsl.net wrote: bob91...@yahoo.com said: But I thought conventional wisdom is that most crystals are AT cut and an attempt at zero average coefficient is made, causing a nonlinear characteristic. But perhaps over a limited range it's linear. The problem of course is calibration. Most crystals are low cost. They will have a temperature characteristic similar to the graph about half way down this URL: http://www.4timing.com/techcrystal.htm The specs on the standard oscillator packages vary from 100ppm to 20ppm. That covers temperature and voltage and initial manufacturing and some amount of aging. (I haven't looked at the spec sheets recently. I don't remember seeing anything about aging.) The point is that they are low cost and the specs are reasonably clear, something a digital designer can understand and use. Again, how does one calibrate those 3 MHz ovenized units? I plug mine into a HP 5334B which is clocked by a TBolt. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
- Original Message - From: Hal Murray hmur...@megapathdsl.net To: Bob Albert bob91...@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com Cc: hmur...@megapathdsl.net Sent: Sunday, March 02, 2014 2:45 AM Subject: Re: [time-nuts] Another atomic clock question bob91...@yahoo.com said: Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. How good is your crystal? Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C If you are running ntpd, turn on loopstats and measure the temperature... http://www.megapathdsl.net/~hmurray/ntp/slope.gif I've been watching a 3 MHz ovenized crystal. It was something like 4 for $25 from ebay. It's a 2 in sq can, over an inch high. It's got a few ppb of noise over minutes/hours and a few more ppb of drift/wander over days/months. It took several weeks to stabilize after power on. -- Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised to find it did not have any foam insulation. Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Nigel, Thank you for your comments. I see the situation a bit more clearly now, and will do some searches on Trimble and GPSDO and so on. Right now I am interested in seeing what my options are, and deciding which way to go. Yes this can become an obsession but I keep reminding myself that it's a hobby and isn't stopping me from eating or sleeping or breathing. I do have fun with it. Recently I bored a couple of visitors showing how my counter and signal generator drifted during warmup but eventually settled within about 10 ppb of one another, within about a half hour. (Both units have 24/7 ovens.) The generator actually accounts for nearly all the drift. The counter is a venerable HP 5245L with 500 MHz plugin. Bob On Sunday, March 2, 2014 10:33 AM, Tom Miller tmiller11...@verizon.net wrote: - Original Message - From: Hal Murray hmur...@megapathdsl.net To: Bob Albert bob91...@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com Cc: hmur...@megapathdsl.net Sent: Sunday, March 02, 2014 2:45 AM Subject: Re: [time-nuts] Another atomic clock question bob91...@yahoo.com said: Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. How good is your crystal? Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C If you are running ntpd, turn on loopstats and measure the temperature... http://www.megapathdsl.net/~hmurray/ntp/slope.gif I've been watching a 3 MHz ovenized crystal. It was something like 4 for $25 from ebay. It's a 2 in sq can, over an inch high. It's got a few ppb of noise over minutes/hours and a few more ppb of drift/wander over days/months. It took several weeks to stabilize after power on. -- Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised to find it did not have any foam insulation. Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
HI If that is what you currently have for references, then you probably need a “lab standard” to drive things. Having one reference for all the gear makes things *much* easier. You don’t have to mess with a lot of “which one’s right today” sort of decisions. That would make the GPSDO pretty much a slam dunk decision. You get both the reference and the calibration all in one box. Bob On Mar 2, 2014, at 2:56 PM, Bob Albert bob91...@yahoo.com wrote: Nigel, Thank you for your comments. I see the situation a bit more clearly now, and will do some searches on Trimble and GPSDO and so on. Right now I am interested in seeing what my options are, and deciding which way to go. Yes this can become an obsession but I keep reminding myself that it's a hobby and isn't stopping me from eating or sleeping or breathing. I do have fun with it. Recently I bored a couple of visitors showing how my counter and signal generator drifted during warmup but eventually settled within about 10 ppb of one another, within about a half hour. (Both units have 24/7 ovens.) The generator actually accounts for nearly all the drift. The counter is a venerable HP 5245L with 500 MHz plugin. Bob On Sunday, March 2, 2014 10:33 AM, Tom Miller tmiller11...@verizon.net wrote: - Original Message - From: Hal Murray hmur...@megapathdsl.net To: Bob Albert bob91...@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com Cc: hmur...@megapathdsl.net Sent: Sunday, March 02, 2014 2:45 AM Subject: Re: [time-nuts] Another atomic clock question bob91...@yahoo.com said: Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. Somewhere there is a discontinuity in accuracy plotted against cost and I don't want to cross that barrier just yet. If I can get 1 ppb without a big increase in cost, I'll take that. How good is your crystal? Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C If you are running ntpd, turn on loopstats and measure the temperature... http://www.megapathdsl.net/~hmurray/ntp/slope.gif I've been watching a 3 MHz ovenized crystal. It was something like 4 for $25 from ebay. It's a 2 in sq can, over an inch high. It's got a few ppb of noise over minutes/hours and a few more ppb of drift/wander over days/months. It took several weeks to stabilize after power on. -- Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised to find it did not have any foam insulation. Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi As long as your resistor keeps the temperature to within a micro degree it will do pretty well. Bob On Mar 2, 2014, at 2:09 PM, Chris Albertson albertson.ch...@gmail.com wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 3/2/14 11:09 AM, Chris Albertson wrote: Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C So does this mean I can epoxy a sandstone power resister to a junk crystal and keep the frequency exactly perfect by varying the power in the resister? Yes.. but you have to hold temperature to 0.001 degree, which is somewhat challenginggrin A lot of SAW devices have tempcos that look like a parabola that fits in a box that is 100 degrees wide, and 100 ppm high. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 3/2/14 12:21 PM, Bob Camp wrote: Hi As long as your resistor keeps the temperature to within a micro degree it will do pretty well. Oh, you were looking for 1E-12.. I was thinking 1E-9 would be good enough. The other issue is that the phase noise might be pretty bad with a cheap crystal, if it's not particularly high Q. Probably not what you want to use if you're multiplying it up for the carrier on your 240GHz narrowband transmitter. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think. Bob On Mar 2, 2014, at 3:40 PM, Jim Lux jim...@earthlink.net wrote: On 3/2/14 12:21 PM, Bob Camp wrote: Hi As long as your resistor keeps the temperature to within a micro degree it will do pretty well. Oh, you were looking for 1E-12.. I was thinking 1E-9 would be good enough. The other issue is that the phase noise might be pretty bad with a cheap crystal, if it's not particularly high Q. Probably not what you want to use if you're multiplying it up for the carrier on your 240GHz narrowband transmitter. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 02/03/14 21:45, Bob Camp wrote: Hi The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think. hysteresis, memory effect, restart of frequency drift Yeah, it puts a limit on how good a TCXO can track-and-compensate. I was also considering the use of XOs for temperature sensing, it has the benefit that it is relatively easy to sense with resolution, but after that frequency/phase measures is in, getting a good temperature reading isn't as easy. Is there a good temperature-sensing set of modes in AT-cut crystals, as I know being used in SC-cut crystals? Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On 3/2/14 1:00 PM, Magnus Danielson wrote: On 02/03/14 21:45, Bob Camp wrote: Hi The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think. hysteresis, memory effect, restart of frequency drift Yeah, it puts a limit on how good a TCXO can track-and-compensate. I was also considering the use of XOs for temperature sensing, it has the benefit that it is relatively easy to sense with resolution, but after that frequency/phase measures is in, getting a good temperature reading isn't as easy. Is there a good temperature-sensing set of modes in AT-cut crystals, as I know being used in SC-cut crystals? There's the scheme which measures the temperature by comparing fundamental and third overtone modes of a crystal. But if you want to measure temperature, a SAW might be one way. You mix the output of a SAW oscillator with a more stable bulk oscillator, and count the difference frequency. Back in the 80s, I worked at a place that made tons of sensors for all sorts of things which either measured a SAW resonator, or measured the difference between two SAW resonators that were back to back (so their temperatures were the same). The sensor depended on what you did to the SAW: bend it, deposit mass on it, etc. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
HI On Mar 2, 2014, at 4:00 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 02/03/14 21:45, Bob Camp wrote: Hi The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think. hysteresis, memory effect, restart of frequency drift” In addition to those there is actually a “temperature rate of change” dependent frequency change coefficient. It varies with the angle of cut and the temperature. Yeah, it puts a limit on how good a TCXO can track-and-compensate. I was also considering the use of XOs for temperature sensing, it has the benefit that it is relatively easy to sense with resolution, but after that frequency/phase measures is in, getting a good temperature reading isn't as easy. Is there a good temperature-sensing set of modes in AT-cut crystals, as I know being used in SC-cut crystals? As Jim mentions in another post, you can run on the fundamental and the third (or 5th or 7th) and get a thermometer out of the delta between the two modes. The gotcha is that a change in load impedance will shift the frequencies unequally. That will give you an apparent temperature change. Bob Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi Bob, On 02/03/14 23:16, Bob Camp wrote: HI On Mar 2, 2014, at 4:00 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 02/03/14 21:45, Bob Camp wrote: Hi The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think. hysteresis, memory effect, restart of frequency drift” In addition to those there is actually a “temperature rate of change” dependent frequency change coefficient. It varies with the angle of cut and the temperature. Indeed. I expect it to be individual to each particular crystal. Yeah, it puts a limit on how good a TCXO can track-and-compensate. I was also considering the use of XOs for temperature sensing, it has the benefit that it is relatively easy to sense with resolution, but after that frequency/phase measures is in, getting a good temperature reading isn't as easy. Is there a good temperature-sensing set of modes in AT-cut crystals, as I know being used in SC-cut crystals? As Jim mentions in another post, you can run on the fundamental and the third (or 5th or 7th) and get a thermometer out of the delta between the two modes. The gotcha is that a change in load impedance will shift the frequencies unequally. That will give you an apparent temperature change. I already know about the fundamental and third trick, my question was if it could be done to AT-cut as well. I interpret your statement as yes, it does. I don't trust it to be perfect, but reasonable. Ideas for means to handle shift would be welcome. I don't have SC-cut crystals lying around, only complete OCXOs. It would be fun to build a simple double-mode oscillator around an AT lying around. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
On Mar 2, 2014, at 5:29 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Bob, On 02/03/14 23:16, Bob Camp wrote: HI On Mar 2, 2014, at 4:00 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 02/03/14 21:45, Bob Camp wrote: Hi The gotcha is that there are second order temperature effects. If you are going to run the crystal very far off turn, you need to keep it more stable than you might think. hysteresis, memory effect, restart of frequency drift” In addition to those there is actually a “temperature rate of change” dependent frequency change coefficient. It varies with the angle of cut and the temperature. Indeed. I expect it to be individual to each particular crystal. There is a body of information that suggests that it’s related to the cut, the same way as the AT (or SC) frequency temperature performance is. It also relates to the mounting, which will vary from part to part. Yeah, it puts a limit on how good a TCXO can track-and-compensate. I was also considering the use of XOs for temperature sensing, it has the benefit that it is relatively easy to sense with resolution, but after that frequency/phase measures is in, getting a good temperature reading isn't as easy. Is there a good temperature-sensing set of modes in AT-cut crystals, as I know being used in SC-cut crystals? As Jim mentions in another post, you can run on the fundamental and the third (or 5th or 7th) and get a thermometer out of the delta between the two modes. The gotcha is that a change in load impedance will shift the frequencies unequally. That will give you an apparent temperature change. I already know about the fundamental and third trick, my question was if it could be done to AT-cut as well. I interpret your statement as yes, it does. I don't trust it to be perfect, but reasonable. Ideas for means to handle shift would be welcome. It was originally proposed by a very nice guy from Ft. Monmouth for use with AT cut resonators. I believe the paper is in the FCS proceedings from the mid 1980’s. The DOD kept rights to the technique and licensed it to a couple of oscillator companies. Bob I don't have SC-cut crystals lying around, only complete OCXOs. It would be fun to build a simple double-mode oscillator around an AT lying around. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
tmiller11...@verizon.net said: Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised to find it did not have any foam insulation. RDR Electronics There were 2 per board, from some old telco/cell gear. http://w9fz.com/ham/s3mhz2.jpg http://w9fz.com/ham/3mhzocxo.txt I have several spares if anybody wants to experiment. I haven't taken one apart. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
As Jim mentions in another post, you can run on the fundamental and the third (or 5th or 7th) and get a thermometer out of the delta between the two modes. The gotcha is that a change in load impedance will shift the frequencies unequally. That will give you an apparent temperature change. I already know about the fundamental and third trick, my question was if it could be done to AT-cut as well. I interpret your statement as yes, it does. I don't trust it to be perfect, but reasonable. Ideas for means to handle shift would be welcome. It was originally proposed by a very nice guy from Ft. Monmouth for use with AT cut resonators. I believe the paper is in the FCS proceedings from the mid 1980’s. The DOD kept rights to the technique and licensed it to a couple of oscillator companies. Hmm. SC cut, perhaps? (see the third reference down.. R. L. Filler and J. R. Vig, “Resonators for the microcomputer compensated crystal oscillator,” 43rd Ann. Symp. Freq. Contr., pp. 8- 15, 1989. there's also The microcomputer compensated crystal oscillator (MCXO) Bloch, M. ; Frequency Electron. Inc., Mitchel Field, NY, USA ; Meirs, M. ; Ho, J. The MCXO uses a novel technique to achieve temperature compensation without the use of ovens or conventional temperature-compensating components. The crystal oscillator in the MCXO, which is free to vary with temperature, operates on two modes simultaneously-the fundamental and the third overtone. Several advantages accrue because this method of temperature compensation does not resort to frequency pulling. The authors presents the details of how the MCXO operates and the details of the performance of the delivered systems Published in: Frequency Control, 1989., Proceedings of the 43rd Annual Symposium on Date of Conference: 31 May-2 Jun 1989 Page(s): 16 - 19 Meeting Date : 31 May 1989-02 Jun 1989 INSPEC Accession Number: 3685419 Conference Location : Denver, CO Digital Object Identifier : 10.1109/FREQ.1989.68853 But then, Yoonkee Kim (from Ft Monmouth) has a paper (DTIC ADA484423) Aging of Dual Mode Resonator for Microcomputer Compensated Crystal Oscillator Abstract— A Microcomputer Compensated Crystal Oscillator (MCXO) utilizes the dual c-mode excitation (fundamental mode and 3rd overtone (OT)) of an SC-cut resonator for self- temperature sensing and compensation. The long-term stability of the MCXO depends primarily on the aging of the dual mode resonator. When two modes age differently in time, the aging MCXO’s output frequency curve would shift with a tilt over its operating temperature range ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi I believe the paper was by Stan Shadowski. I’m *certain* I’ve mis-spelled his last name, which is indeed a very poor move on my part. I would not be surprised if there are several co-authors. I don’t have the UFC indexes here at home so I have no quick way to look it up. Bob On Mar 2, 2014, at 7:40 PM, Jim Lux jim...@earthlink.net wrote: As Jim mentions in another post, you can run on the fundamental and the third (or 5th or 7th) and get a thermometer out of the delta between the two modes. The gotcha is that a change in load impedance will shift the frequencies unequally. That will give you an apparent temperature change. I already know about the fundamental and third trick, my question was if it could be done to AT-cut as well. I interpret your statement as yes, it does. I don't trust it to be perfect, but reasonable. Ideas for means to handle shift would be welcome. It was originally proposed by a very nice guy from Ft. Monmouth for use with AT cut resonators. I believe the paper is in the FCS proceedings from the mid 1980’s. The DOD kept rights to the technique and licensed it to a couple of oscillator companies. Hmm. SC cut, perhaps? (see the third reference down.. R. L. Filler and J. R. Vig, “Resonators for the microcomputer compensated crystal oscillator,” 43rd Ann. Symp. Freq. Contr., pp. 8- 15, 1989. there's also The microcomputer compensated crystal oscillator (MCXO) Bloch, M. ; Frequency Electron. Inc., Mitchel Field, NY, USA ; Meirs, M. ; Ho, J. The MCXO uses a novel technique to achieve temperature compensation without the use of ovens or conventional temperature-compensating components. The crystal oscillator in the MCXO, which is free to vary with temperature, operates on two modes simultaneously-the fundamental and the third overtone. Several advantages accrue because this method of temperature compensation does not resort to frequency pulling. The authors presents the details of how the MCXO operates and the details of the performance of the delivered systems Published in: Frequency Control, 1989., Proceedings of the 43rd Annual Symposium on Date of Conference: 31 May-2 Jun 1989 Page(s): 16 - 19 Meeting Date : 31 May 1989-02 Jun 1989 INSPEC Accession Number: 3685419 Conference Location : Denver, CO Digital Object Identifier : 10.1109/FREQ.1989.68853 But then, Yoonkee Kim (from Ft Monmouth) has a paper (DTIC ADA484423) Aging of Dual Mode Resonator for Microcomputer Compensated Crystal Oscillator Abstract— A Microcomputer Compensated Crystal Oscillator (MCXO) utilizes the dual c-mode excitation (fundamental mode and 3rd overtone (OT)) of an SC-cut resonator for self- temperature sensing and compensation. The long-term stability of the MCXO depends primarily on the aging of the dual mode resonator. When two modes age differently in time, the aging MCXO’s output frequency curve would shift with a tilt over its operating temperature range ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
There are WWVB clocks with serial output. Arcron made one that I added linux ntp support for some years back. http://www.atomictimeclock.com/radsynarcron.htm http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver27.html As I recall, it was under $100, quite nicely styled, and is sitting here on my desk. (Reception on the East Coast can be spotty, so I've switched to standard internet net time source). On Mon, Feb 24, 2014 at 7:44 AM, Bob Camp li...@rtty.us wrote: Hi Ok, so 0.1 second at the sync point is indeed a reasonable estimate. If that's all you need to deal with (you correct out the crystal offset one way or the other) then: At 1 day you have 11.5 ppm accuracy. Roughly a 100 Hz beat note with WWV at 10 MHz. At 10 days you have 1.15 ppm. Roughly a 1 Hz beat note at 10 MHz. At 100 days you have 0.115 ppm. That would be about a 10 second period beat note. None of that is to say that a beat note is all there is to getting accuracy off of WWV or that the two approaches deliver the same net accuracy. Yes I've done the 10 second beat thing, it can be done with care and a good stable WWV signal. Bob On Feb 23, 2014, at 5:21 PM, Tom Van Baak t...@leapsecond.com wrote: Now that you have brought up this subject, do you know of any way to use these LaCrosse clocks to calibrate frequency standards? I suggest using a direct electric (1.5 VDC high-Z) or indirect magnetic (high gain) pickup on the coil to get the +/- pulse per second. Compare this time with your local frequency standard and over several days you should get accuracy better than 10 ms per day (1e-7). Here's an example of a raw phase plot: http://leapsecond.com/pages/Junghans/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
All this is very interesting. However, my interest is frequency. In other words, I want to know that my standard oscillators are as close to desired frequency as possible, and how close that turns out to be. Yes, the Internet gives me time of day as close as I care to know. I have an 'atomic' clock from LaCrosse that resets itself nightly, although it's fussy about where in the house I put it. If I put it where I'd like, it won't receive WWVB, so I put it across the room. I called the company inquiring about augmenting the internal antenna but they were of no help. While watching the clock and listening to WWV, it seems the clock is a fraction of a second behind. Even that doesn't matter, but calibrating the counter time base is another kind of thing. I am trying to understand how this is done. Should I ever get a rubidium standard, I'd want to check its calibration, and that's not a trivial exercise. Bob On Saturday, March 1, 2014 4:56 PM, Paul Alfille paul.alfi...@gmail.com wrote: There are WWVB clocks with serial output. Arcron made one that I added linux ntp support for some years back. http://www.atomictimeclock.com/radsynarcron.htm http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver27.html As I recall, it was under $100, quite nicely styled, and is sitting here on my desk. (Reception on the East Coast can be spotty, so I've switched to standard internet net time source). On Mon, Feb 24, 2014 at 7:44 AM, Bob Camp li...@rtty.us wrote: Hi Ok, so 0.1 second at the sync point is indeed a reasonable estimate. If that's all you need to deal with (you correct out the crystal offset one way or the other) then: At 1 day you have 11.5 ppm accuracy. Roughly a 100 Hz beat note with WWV at 10 MHz. At 10 days you have 1.15 ppm. Roughly a 1 Hz beat note at 10 MHz. At 100 days you have 0.115 ppm. That would be about a 10 second period beat note. None of that is to say that a beat note is all there is to getting accuracy off of WWV or that the two approaches deliver the same net accuracy. Yes I've done the 10 second beat thing, it can be done with care and a good stable WWV signal. Bob On Feb 23, 2014, at 5:21 PM, Tom Van Baak t...@leapsecond.com wrote: Now that you have brought up this subject, do you know of any way to use these LaCrosse clocks to calibrate frequency standards? I suggest using a direct electric (1.5 VDC high-Z) or indirect magnetic (high gain) pickup on the coil to get the +/- pulse per second. Compare this time with your local frequency standard and over several days you should get accuracy better than 10 ms per day (1e-7). Here's an example of a raw phase plot: http://leapsecond.com/pages/Junghans/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
