Re: [time-nuts] is there a best bet advanced hobbyist buildable GPSDOdesign?
Bruce Griffiths wrote: michael taylor wrote: You have made similar comments about I believe the same approach in the past. I was wondering if you have ever sketched out a schematic, even if only rough. Perhaps with a few suggested components to try (i.e. DAC, Op-Amp) that would be a good starting point for anyone who wanted to prototype and evaluate the performance of this approach. It is beyond my elementary design abilities to convert your description into a well implemented design on my own, but I would be interested in try to at least see if I could construct an unit using these suggested techniques. -Michael Michael Attached is the circuit for a 1 bit phase detector. HCMOS should be perfectly adequate given that the flipflop is allowed several hundred millisec to settle before being read by the microprocessor. An RF transformer isolated clock shaper should be used to shape the OCXO output and avoid low frequency ground loops. You probably want at least a 2 output distribution amplifier (unless your OCXO has multiple isolated outputs eg FTS1200 OSA8607, some of the Wenzel OCXOs, etc.) to allow the OCXO output to be used for other applications as well. The position of the divider output transition is adjusted by the control algorithm with respect to the leading edge of the PPS signal so that the D flipflop Q has a 50% chance of being 1 when read by the microprocessor. The effective resolution is determined by the jitter of the leading edge of the PPS pulse. Bruce 1BitPhaseDetector.pdf Description: Adobe PDF 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] Fury Interface Board simulation results
Thanks, Bruce, for the circuit. I don't recognize the transformer numbers in your schematic. Can you tell us more about the nature of the transformers you have specified? Bruce Griffiths wrote: George The circuit schematic for a BJT version of the JFET frequency is attached. The biasing is a little more complex as it is necessary set each frequency doubler BJT collector current at about 1mA or so to maximise conversion gain. The input impedance is also around 50 ohms. Have also minimised the number of different component values used. Other transistors may be substituted but some care is required as the reverse voltage across the base emitter junction is about 2V for a +13dBm input. Some filtering of the output waveform is required. The intended output load is 50 ohms. The 200 ohm emitter series resistors together with the transformed source impedance ensure that there is sufficient degeneration to keep the phase noise low. Obtaining suitable transistors for this circuit should be much easier than obtaining suitable JFETS for the JFET doubler. Whilst a diode doubler (at higher frequencies this may be the only sensible option) could be used it would need both an input amplifier and an output amplifier. Bruce ___ 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] Fury Interface Board simulation results
Rex wrote: Thanks, Bruce, for the circuit. I don't recognize the transformer numbers in your schematic. Can you tell us more about the nature of the transformers you have specified? Rex These are standard Minicircuits through hole mount RF transformers that have (with an appropriate termination) low VSWR for frequencies around 5-10MHz or so. They also make surface mount equivalents. They have impedance ratios of 16:1 (4:1 turns ratio centre tapped on the high impedance side). Although a centre tapped transformer isnt needed for the output I elected to use the same part to keep the number of different parts down especially when they appear very similar. Bruce ___ 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] Fury Interface Board simulation results
Thanks. Great! Commonly available part.. I agree one part for both is good. Bruce Griffiths wrote: Rex wrote: Thanks, Bruce, for the circuit. I don't recognize the transformer numbers in your schematic. Can you tell us more about the nature of the transformers you have specified? Rex These are standard Minicircuits through hole mount RF transformers that have (with an appropriate termination) low VSWR for frequencies around 5-10MHz or so. They also make surface mount equivalents. They have impedance ratios of 16:1 (4:1 turns ratio centre tapped on the high impedance side). Although a centre tapped transformer isnt needed for the output I elected to use the same part to keep the number of different parts down especially when they appear very similar. Bruce ___ 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] need recomendation for a portable 10mhz reference oscilator
From: bg [EMAIL PROTECTED] Subject: Re: [time-nuts] need recomendation for a portable 10mhz reference oscilator Date: Wed, 12 Dec 2007 06:58:15 +0100 Message-ID: [EMAIL PROTECTED] On Tue, 2007-12-11 at 18:38 -0500, John Ackermann N8UR wrote: To get decent (for some definition of decent) timing, you need to operate the receiver in 0-D mode, telling it where it is and letting it solve just for time. I haven't done the experiments myself but I believe that the time accuracy is pretty dramatically degraded when operating in 2-D or 3-D mode. How long does a survey take (in good conditions) and what sort of time constant would you want to use with a navigation box? It depends on the receiver, but usually it's a few hours to a full day. Of course, if you use external software you can use whatever time period you want. John I am surprised surveying mode is needed anymore. In a SA environment it makes sense, but for me its hard to understand with the current accuracy given by the GPS system. For the 2,13E-9 precission needed, very simple arrangements should be needed around a standard GPS receiver. No fancy features like sawtooth correction and TRAIM needed. My little bluetooth-GPS would do after a very mild modification (PPS output). If you use a OSA 8712 together with a simple GPS, only very simple control should be needed. Powerbudget and price could be held fairly low. The optimum design does not always relate to optimum Allan Deviation curve you know. :) 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] Fury Interface Board simulation results
Rex wrote: Thanks. Great! Commonly available part.. I agree one part for both is good. Rex One caveat is the dc current flowing in the output transformer may cause too much distortion (actual specification on the data sheet is somewhat unclear/ambiguous), in which case capacitively coupling the output transformer and using an inductive shunt feed arrangement will cure this problem. Of course the ideal location for series tuned shunt traps (tuned to fundamental and say 4th harmonic) is from the output collectors to ground. These short unwanted harmonic currents to ground allowing a relatively simple low pass filter to be used to cleanup the output without contributing significant phase shift and associated tempco to the desired second harmonic output. The net dc current flowing in the input transformer secondary will be very small. Bruce ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Hi Bruce, Fine, you don't like the words far better performance... okay ;-) you do recognize the small advantage in noise but gave no relevance to the other aspects namely the lock acquisition, the fact that I can monitor the jitter over time etc. (all of them were contained in my word performance not just the noise). you wrote, By all means try them, Humm?! I did tried them, that's exactly what I said !!! Note that I do have the hardware on a CPLD so schemes can be done on type-compile-and-test basis without soldering wires hi ;-) but why add the power consumption and complexity of a CPLD if it offers little improvement in performance? G, using a CPLD does not add complexity, it is just one chip and it offers the commodity of being easily configured etc. Also the power consumption is surely not an issue, if you are not happy with the 50 to 100mA you may draw from 3.3v just use a low power CPLD (like tha maxIIZ) and get only 10 to 20mA. On the comments about the filter and bandwidth I do agree with you it would be good to have most of it digital (doesn't need to be necessarily on a CPU... inside the CPLD is the same) I do have versions with integration also in digital and I'm still in the process of improving it. I believe I may get rid off of some of the inconvenient analog filtering, in the next VHDL iterations hi ;-) One thing is puzzling me, if you suggest using a single D flip-flop and want it simple as you say I presume you have also to filter in analog ?! So you end up with a slightly worst phase comparator and the less convenient analog filter :-( Or do you need to add a microcontroller and a DAC ? If that is the case, there goes off your complexity issue much higher than a simple CPLD. Luis Cupido. ct1dmk ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Luis Cupido wrote: Hi Bruce, Fine, you don't like the words far better performance... okay ;-) you do recognize the small advantage in noise but gave no relevance to the other aspects namely the lock acquisition, the fact that I can monitor the jitter over time etc. (all of them were contained in my word performance not just the noise). Its not too difficult to add a couple of extra flipflops plus associated delays to allow reasonably accurate estimation of noise if thats useful. you wrote, By all means try them, Humm?! I did tried them, that's exactly what I said !!! Note that I do have the hardware on a CPLD so schemes can be done on type-compile-and-test basis without soldering wires hi ;-) A theoretical understanding the performance tradeoffs can save a lot of time and effort. but why add the power consumption and complexity of a CPLD if it offers little improvement in performance? G, using a CPLD does not add complexity, it is just one chip and it offers the commodity of being easily configured etc. Also the power consumption is surely not an issue, if you are not happy with the 50 to 100mA you may draw from 3.3v just use a low power CPLD (like tha maxIIZ) and get only 10 to 20mA. You have to keep in mind that not everyone on this list can or wants to program a CPLD. On the comments about the filter and bandwidth I do agree with you it would be good to have most of it digital (doesn't need to be necessarily on a CPU... inside the CPLD is the same) I do have versions with integration also in digital and I'm still in the process of improving it. I believe I may get rid off of some of the inconvenient analog filtering, in the next VHDL iterations hi ;-) One thing is puzzling me, if you suggest using a single D flip-flop and want it simple as you say I presume you have also to filter in analog ?! Where did you get that from?? No analog filtering of the D flipflop output is required. So you end up with a slightly worst phase comparator and the less convenient analog filter :-( Try reading up on how the radio astronomers digitise their noise like signals. You should also look at why a 1-2 bit ADC suffices for most GPS timing receivers. Or do you need to add a microcontroller and a DAC ? If that is the case, there goes off your complexity issue much higher than a simple CPLD. I've used plenty of CPLDs but see no reason to use one when it isnt necessary. If you want really high phase measurement resolution then the high noise internal environment of a CPLD can add plenty of jitter and unwanted crosstalk. You are unlikely to ever achieve a jitter of 10picosec or less with a standard CPLD whereas this is readily achieved using a single flipflop or a wideband ADC used as a phase detector. Luis Cupido. ct1dmk Bruce ___ 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] Using a Vectron OCXO 5mhz oscilator with ntpd
I have started to see this 5mhz frequency quartz oscilators that are really inexpensive (see http://www.alltronics.com/cgi-bin/ category.cgi?item=04P010 ). My question, how would you get this to work with ntpd? Seems like it work great for my situation where I can just put inside the rack behind the server, use some ntp servers to get the time to within 1 msec usually and then use this to get into the nanosecond accuracy. There are two issues with keeping time. The first is to get your clock to tick at the right frequency, or to know how fast your clock is actually ticking. ntpd is pretty good at that. If you haven't done it already, turn on loopstats and graph the offset and drift columns. The drift is basically the difference between the nominal frequency and the measured frequency, aka the inaccuracy of the crystal. Most crystals make reasonable thermometers. The other issue is lining up the seconds ticks. You can get reasonable results by asking nearby ntp servers that know the answer. How good you get depends mostly on your network connection. If you want better than a few milliseconds, you need a local PPS source. If you want to get started, I recommend the Garmin GPS 18 LVC. Under $100. Some soldering required. Not much. (It needs 5V. You can get it from USB.) http://support.ntp.org/bin/view/Support/ConfiguringGarminRefclocks I got mine at ProVantage.com There are some on eBay, but the picture is the USB version. You want the OEM version - without maps or software. The main advantage you will get from a good OCXO will be that ntpd doesn't have to spend any time tracking the thermal drift of your local crystal. You still need to find the seconds ticks. -- These are my opinions, not necessarily my employer's. 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Bruce, I've used plenty of CPLDs but see no reason to use one when it isnt necessary. The sentence in my perspective sounds a bit like this: I've used plenty of TTL and CMOS but see no reason to use them when I could fit them all on a CPLD. I do understand that some may not want to get into this kind of devices, however I see not much of a difference of learning you way with microcontrollers, CPLDs or with any digital IC's these days. CPLDs in general do bring simplicity but do require learning how to use them and for various reasons that may be undesirable and be confused with a complexity issue while it is just a learning issue. Very good, I do respect the usage of a bunch of CMOS/TTL chips if someone doesn't want to spend the effort of learning how to use a CPLD. When it comes to use CPUs for tasks better done by straight logic (and there are many examples out there) then I think it is not the right option. All understood so let's not discuss that any further. --- No analog filtering of the D flipflop output is required. Now you got me lost. We were talking about a GPSDO, that is locking an VCXO on the GPS time (1pps or else) So by the end of it you need an analog signal to control the voltage input of the VCXO. Right ? Where you get that from ? If not by filtering your flip-flop output what else you have in between the 1pps and the VCXO ? CPU's DAC's if so how does your complexity arguments still apply ? Luis Cupido ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
On Dec 12, 2007 7:33 AM, Luis Cupido [EMAIL PROTECTED] wrote: Very good, I do respect the usage of a bunch of CMOS/TTL chips if someone doesn't want to spend the effort of learning how to use a CPLD. When it comes to use CPUs for tasks better done by straight logic (and there are many examples out there) then I think it is not the right option. All understood so let's not discuss that any further. Bruce also alludes to the higher jitters of CPLD versus Advanced/High Speed CMOS logic gates (AC or HC families). This has to do with the programmable nature of CPLD / FPGA ICs as I understand it. Ref: http://www.febo.com/pipermail/time-nuts/2007-April/025299.html -Michael ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Bruce Griffiths wrote: Do you also want a circuit for a sawtooth corrector using one of the Maxim/Dallas programmable delay lines? Yes! I now feel inspired to go spin a design after studying all of these messages in this thread. My only constraint is that the parts have to pass the Digikey test, i.e. I have to be able to order small quantities from Digikey, Mouser, or the like. It's nearly impossible for a hobbyist like me to get small quantities of more exotic parts. The big distributors have gotten better in the last decade about taking small orders, but still often have minimum qty/piece requirements that they won't waive. Even worse are orderable, but unobtainable parts -- Maxim seems to have a huge library of such virtual chips that have lead times of 1/2 year or more. Scott ___ 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] Time hackers
http://www.wired.com/science/discoveries/news/2007/12/time_hackers 73 Alberto I2PHD ___ 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] Big Picture View
Keith E. Brandt, M.D. wrote: As a relative newbie to the who time-nut scene, I'm still working on the big picture of how all the hardware fits together. I've successfully put together a FreeBSD box with a Garmin 18 LVC as an NTP server and am getting consistent microsecond accuracy. I've been looking at the next step of adding a stable oscillator to the system. I'm not seeing how to integrate this into the system. The way I understand it, the oscillator is there to provide a very stable frequency reference, regardless of the type used -- VXCO, rubidium, cesium, etc. What I'm not seeing is how you link the frequency reference to UTC. For NTP, I'm guessing that you'd have to sync a PPS pulse with a known time source such as GPS. Am I on the right track? Pointers to references appreciated. 73, Keith Hi Keith -- Frequency isn't linked to UTC; phase is. What you're doing with an external oscillator is simply providing the computer with a stable clock frequency. The PPS signal from the GPS provides the phase information that tells NTP when the second marker is. The stable clock frequency just makes it easier for NTP to hold the second marker at the proper point. Even if the reference frequency is inaccurate (and that may be the question your asking), NTP is still better off as it can correct for a frequency offset more easily than it can a clock that is erratic. Hope this helps. 73, John ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Luis Cupido wrote: Bruce, No analog filtering of the D flipflop output is required. Now you got me lost. We were talking about a GPSDO, that is locking an VCXO on the GPS time (1pps or else) So by the end of it you need an analog signal to control the voltage input of the VCXO. Right ? Where you get that from ? If not by filtering your flip-flop output what else you have in between the 1pps and the VCXO ? CPU's DAC's Some software, including a sigma delta DAC, the effect of which is no different, in principle, than the filtering etc required by any of your phase detector implementations. The 1 bit phase error samples are processed in software (or hardware depending on one's inclinations, expertise, etc) in a similar way that samples from an N (1) phase detector samples are, to produce a digital output for a DAC which drives the OCXO EFC input. The only difference is that a sigma delta DAC is used instead of a conventional DAC. if so how does your complexity arguments still apply ? The interpretation of complexity depends on ones background and experience. The originator of the thread indicated that they had some microprocessor software experience. Luis Cupido I was trying to tailor the design to the stated strengths of the originator of the thread. If one is trying to squeeze the ultimate in performance when using a GPS receiver to discipline an OCXO, then carrier phase measurements potentially offer much higher performance than can be achieved by using the PPS output of a typical GPS timing receiver. However only a few commercially available GPS receivers are suitable for this application. The GPS receiver oscillators all have to be phase locked to the OCXO being disciplined. This approach has been used in at least one commercially available GPSDOCXO. In principle a GPS receiver has all the required measurement hardware, so all that is required are suitable algorithms implemented in either software running on a DSP, microprocessor, etc, or implemented in hardware (CPLD etc). Bruce ___ 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] Big Picture View
John, That's a good start towards answering my question. Given my set-up of GPS referenced NTP server, how would I integrate a frequency reference into the system? Keith As a relative newbie to the who time-nut scene, I'm still working on the big picture of how all the hardware fits together. I've successfully put together a FreeBSD box with a Garmin 18 LVC as an NTP server and am getting consistent microsecond accuracy. I've been looking at the next step of adding a stable oscillator to the system. I'm not seeing how to integrate this into the system. The way I understand it, the oscillator is there to provide a very stable frequency reference, regardless of the type used -- VXCO, rubidium, cesium, etc. What I'm not seeing is how you link the frequency reference to UTC. For NTP, I'm guessing that you'd have to sync a PPS pulse with a known time source such as GPS. Am I on the right track? Pointers to references appreciated. 73, Keith Hi Keith -- Frequency isn't linked to UTC; phase is. What you're doing with an external oscillator is simply providing the computer with a stable clock frequency. The PPS signal from the GPS provides the phase information that tells NTP when the second marker is. The stable clock frequency just makes it easier for NTP to hold the second marker at the proper point. Even if the reference frequency is inaccurate (and that may be the question your asking), NTP is still better off as it can correct for a frequency offset more easily than it can a clock that is erratic. Hope this helps. 73, John ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Scott Burris wrote: Bruce Griffiths wrote: Do you also want a circuit for a sawtooth corrector using one of the Maxim/Dallas programmable delay lines? Yes! I now feel inspired to go spin a design after studying all of these messages in this thread. My only constraint is that the parts have to pass the Digikey test, i.e. I have to be able to order small quantities from Digikey, Mouser, or the like. It's nearly impossible for a hobbyist like me to get small quantities of more exotic parts. The big distributors have gotten better in the last decade about taking small orders, but still often have minimum qty/piece requirements that they won't waive. Even worse are orderable, but unobtainable parts -- Maxim seems to have a huge library of such virtual chips that have lead times of 1/2 year or more. Scott Scott I usually checkout the availability of parts in small quantity from such sources, although which suppliers to check depends on your location. Locally RS Components and Farnell are very good (they are also good sources in Europe). I have a Digikey printed catalog with prices in my local currency($NZ) (I have ordered a few things from them when I cant easily get them locally). Linear Technologies on line ordering facility works well for some of their more exotic parts and evaluation kits. As far as I know Dallas/Maxim appears to be the only source of suitable affordable programmable delay chips for this particular application. In principle one could use a tapped chain of gates in a CPLD, however continuous calibration of the delay is required (a delay locked loop controlling the gate propagation delay by adjusting its power supply voltage to compensate for the effect of temperature variations is one technique). However unless the Dallas chips become hard to obtain its probably best to leave this as a backup option. What processor are you intending to use to decipher the sawtooth correction messages from the GPS timing receiver? You could use an inexpensive microprocessor dedicated to this simple task. Another microprocessor can be used to discipline the OCXO. Depending on your experience, this can be easier than using a single microprocessor to do everything. Bruce ___ 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] Big Picture View
Keith E. Brandt, M.D. wrote: John, That's a good start towards answering my question. Given my set-up of GPS referenced NTP server, how would I integrate a frequency reference into the system? You'd replace the crystal oscillator on the motherboard with a more stable reference. The TAPR Clock-Block (http://www.tapr.org/kits_clock-block.html) is a synthesizer designed for that purpose; it can take a 5 or 10 or whatever MHz input signal and convert it to the clock frequency needed by the motherboard. An example of doing this is at http://www.febo.com/pages/soekris where I convert a single board computer into a very precise timekeeper using a Clock-Block and some other hardware hacks. John ___ 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] need recomendation for a portable 10mhz reference oscilator
In a message dated 12/11/2007 22:00:37 Pacific Standard Time, [EMAIL PROTECTED] writes: I am surprised surveying mode is needed anymore. In a SA environment it makes sense, but for me its hard to understand with the current accuracy given by the GPS system. -- Björn Hi Bjoern, even with a very good M12M or M12+ receiver we will typically see some variation of the averaged position over it's ~3 hour (default) auto-survey interval. I've seen altitude change by a meter or two for example. Those couple of nanoseconds may be insignificant when compared to older GPS receiver performance (VP Oncore etc), but if one has the time, why not get the best position average possible. I did also note that it does make a difference if the Auto Survey is done during the day, at dawn, or during the night etc. Might be caused by multipath etc. A 12 hour or 24 hour Auto Survey may reduce the Diurnal effects. We recently added a command to our Fury firmware that allows the user to set any time from 1s to 10,000s for the Auto Survey process to finish. This was done because the differences are so small between any given single-second position, and an auto-surveyed position (less than 5 meters or so). The error due to this is much less than 100ns which is more than adequate for a lot of applications. We have some customers that want the unit to do only 3 to 5 minutes of Auto Surveying for a particular mobile military application, and the resulting 100ns UTC accuracy is way better than their requirement. In that case the Auto Survey time is insignificant when compared to the OCXO warmup time. It all depends on your particular accuracy requirement. bye, Said **See AOL's top rated recipes (http://food.aol.com/top-rated-recipes?NCID=aoltop000304) ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Scott Burris wrote: Yes! I now feel inspired to go spin a design after studying all of these messages in this thread. My only constraint is that the parts have to pass the Digikey test, i.e. I have to be able to order small quantities from Digikey, Mouser, or the like. It's nearly impossible for a hobbyist like me to get small quantities of more exotic parts. The big distributors have gotten better in the last decade about taking small orders, but still often have minimum qty/piece requirements that they won't waive. Even worse are orderable, but unobtainable parts -- Maxim seems to have a huge library of such virtual chips that have lead times of 1/2 year or more. Scott Scott On checking the Mouser and Digikey websites the DS1020 series programmable delay lines are non stock items. However I can obtain the DS1020-25 locally from RS Components. The D1020-15 would be preferable for use with an M12M GPS timing receiver, however the DS1020-25 could be used. Maybe we need to consider using a CPLD or another implementation (eg ramp generator plus DAC (8bit) and comparator). Analog Devices used to make a single chip implementation of the ramp plus DAC and comparator programmable delay system. However such devices need to be calibrated, preferably continuously. The saving grace is that with a dedicated processor, there's plenty of time and processing power to do this once a second (between successive PPS pulses). Calibration technique is simple: 1) Adjust the programmed delay so that the programmed delay is exactly 1 (OCXO) clock period record the DAC data required to achieve this. 2) Adjust the programmed delay so that the programmed delay is exactly 2 (OCXO) clock periods, record the DAC data required to achieve this. 3) calculate the OFFSET and GAIN parameters from the above data. Of course such a scheme can be elaborated to include delays greater than a couple clock periods and exponential averaging of results can be employed to reduce the noise. The calibration technique assumes that the delay is a linear function of the DAC input. A D flipflop plus some additional logic (synchroniser) can be used to detect coincidence between the clock edge and the output of the delay device. Bruce ___ 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] need recomendation for a portable 10mhz referenceoscilator
Hi Said and All I have been following this thread with a lot of interest because my application is also in portable Microwave operations with narrowband modes such as WSJT. The main issue here is not so much long term frequency stability as one only has to find a signal in an SSB passband, but the short-term stability should preferably be better than a few Hz over a 46 second transmission. A second issue as others have mentioned is that one needs to have a stable signal at a new location within a relatively short period for many rover operations (say 15 mins). (Note: I earlier asked a question about short term stability with my Trimble Min-T and this has been solved by increasing the Time constant from the default value of 10 seconds to 200 seconds. The short-term stability is now better than one part in 10^10 which is the limit to which I can measure) Now to my Question: I note the importance of the self survey for absolute time but I wonder if a self survey is important for accurate frequency where the absolute time is not an issue? There are number of things that it seems one could do to achieve frequency stability as fast as possible at a new location. 1. Run the Oven off batteries full time - this can be typically only 3 to 5 watts - for the Mini-T or the Fury. 2. Record the EFC voltage at the home location and insert this in software as starting point at the portable location. 3. Insert the position information in software of the portable location as a staring point. 4. As Said suggests run a short self survey of only a few minutes. Now I am not sure which of any of the above points are necessary or important but I would be grateful for the thoughts of others. Regards Rex VK7MO We have some customers that want the unit to do only 3 to 5 minutes of Auto Surveying for a particular mobile military application, and the resulting 100ns UTC accuracy is way better than their requirement. In that case the Auto Survey time is insignificant when compared to the OCXO warmup time. It all depends on your particular accuracy requirement. bye, Said **See AOL's top rated recipes (http://food.aol.com/top-rated-recipes?NCID=aoltop000304) ___ 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] need recomendation for a portable 10mhz referenceoscilator
In a message dated 12/12/2007 14:11:50 Pacific Standard Time, [EMAIL PROTECTED] writes: Now I am not sure which of any of the above points are necessary or important but I would be grateful for the thoughts of others. Regards Rex VK7MO Hi Rex, that's a lot of great information! Since you are not too concerned about overall frequency accuracy (I assume 1 to 5E-09 would be acceptable) you may not need to or want to lock to GPS at all. With a typical OCXO retrace of 5E-09 you would have a (fairly stable) frequency offset of 235Hz or so at 47GHz. As you mentioned your requirement to be ~2Hz deviation at 47GHz this calculates to about 4.3E-011 stability over 46 seconds. GPS itself cannot deliver that, but a good OCXO flywheel will do that. Any GPSDO with ADEV better than 5E-011 should be sufficient locked to GPS or not, but you may have to keep the oven on at all times as you said. Tom measured the Fury's ADEV (double oven) to achieve this performance above measurement intervals of 0.01 seconds already so that should work really well, and in this short time frame (46 seconds) it's pretty much all up to the OCXO (aging and tempco correction by the processor should not be a factor at 46s intervals either). Thus a good MTI double oven OCXO should do the trick for you and GPS locking is not really needed, except maybe for getting initial frequency accuracy. The advantage of this is that a typical MTI Eurocan double-oven OCXO consumes only about 1.7W and can thus be safely and easily powered by a car battery. bye, Said **See AOL's top rated recipes (http://food.aol.com/top-rated-recipes?NCID=aoltop000304) ___ 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] need recomendation for a portable 10mhz referenceoscilator
Rex Moncur wrote: Hi Said and All I have been following this thread with a lot of interest because my application is also in portable Microwave operations with narrowband modes such as WSJT. The main issue here is not so much long term frequency stability as one only has to find a signal in an SSB passband, but the short-term stability should preferably be better than a few Hz over a 46 second transmission. A second issue as others have mentioned is that one needs to have a stable signal at a new location within a relatively short period for many rover operations (say 15 mins). (Note: I earlier asked a question about short term stability with my Trimble Min-T and this has been solved by increasing the Time constant from the default value of 10 seconds to 200 seconds. The short-term stability is now better than one part in 10^10 which is the limit to which I can measure) Now to my Question: I note the importance of the self survey for absolute time but I wonder if a self survey is important for accurate frequency where the absolute time is not an issue? There are number of things that it seems one could do to achieve frequency stability as fast as possible at a new location. 1. Run the Oven off batteries full time - this can be typically only 3 to 5 watts - for the Mini-T or the Fury. 2. Record the EFC voltage at the home location and insert this in software as starting point at the portable location. 3. Insert the position information in software of the portable location as a staring point. 4. As Said suggests run a short self survey of only a few minutes. Now I am not sure which of any of the above points are necessary or important but I would be grateful for the thoughts of others. Regards Rex VK7MO Rex If you make provision for multiple power sources with preassigned priority its not necessary to run of a battery all the time, however the battery needs to be present as a backup when the other power supplies are disconnected. Achieving this without disturbing the power supply voltages when switching between various power sources requires careful design, a simple diode OR circuit is in general inadequate particularly if more than 2 sources (mains, external dc, internal battery) are available, however the required circuity need not be overly complex. Bruce Bruce ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Bruce Griffiths wrote: As far as I know Dallas/Maxim appears to be the only source of suitable affordable programmable delay chips for this particular application. In principle one could use a tapped chain of gates in a CPLD, however continuous calibration of the delay is required (a delay locked loop controlling the gate propagation delay by adjusting its power supply voltage to compensate for the effect of temperature variations is one technique). However unless the Dallas chips become hard to obtain its probably best to leave this as a backup option. What about sending the 1PPS signal through a number of HC family gates and using a mux to select a tap -- is that better than using a CPLD? Hmm, probably the delay varies too much from manufacturer to manufacturer to make this work reliably. Probably temperature sensitive too. What kind of delay characteristics are needed? I see some other delay lines with 100ps steps available, see: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=408-1127-ND and put that through a mux? Looks like some of the DS1020's are available through Maxim's e-commerce site, but some have a 15 week lead time, depending on the particular model. What processor are you intending to use to decipher the sawtooth correction messages from the GPS timing receiver? You could use an inexpensive microprocessor dedicated to this simple task. Another microprocessor can be used to discipline the OCXO. Depending on your experience, this can be easier than using a single microprocessor to do everything. I have experience with PICs, Atmel AVRs, and various ARM flavors, and limited experience with SOC processors in Xilinx FPGAs (Picoblaze and the like). PICs and AVRs are cheap, so no problem dedicating one to this task. Anyone have a list of GPS units which provide sawtooth correction data? I have a few flavors of Motorola products and a Trimble Lassen IQ laying around. They all provide 1PPS signals, but I bet some don't have the necessary features. Scott ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Hi Michael, Yes that may be true (but I did not test any of that...) Well... with digital prog. logic devices that operate at similar speed than HC and AC should be true yes. On the fast CPLDs that run past 300MHz the jitter should have scale down proportionally (I imagine) but I have no clue if that is similar, better or still worst than HC or AC. Yeap... Nice thing to test Hummm... I'm still thinking how to test such... :-) Luis Cupido. ct1dmk. michael taylor wrote: On Dec 12, 2007 7:33 AM, Luis Cupido [EMAIL PROTECTED] wrote: Very good, I do respect the usage of a bunch of CMOS/TTL chips if someone doesn't want to spend the effort of learning how to use a CPLD. When it comes to use CPUs for tasks better done by straight logic (and there are many examples out there) then I think it is not the right option. All understood so let's not discuss that any further. Bruce also alludes to the higher jitters of CPLD versus Advanced/High Speed CMOS logic gates (AC or HC families). This has to do with the programmable nature of CPLD / FPGA ICs as I understand it. Ref: http://www.febo.com/pipermail/time-nuts/2007-April/025299.html -Michael ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Ok. I understand now what you suggest. Thanks for the explanation. Luis Cupido. ct1dmk. Bruce Griffiths wrote: Luis Cupido wrote: Bruce, No analog filtering of the D flipflop output is required. Now you got me lost. We were talking about a GPSDO, that is locking an VCXO on the GPS time (1pps or else) So by the end of it you need an analog signal to control the voltage input of the VCXO. Right ? Where you get that from ? If not by filtering your flip-flop output what else you have in between the 1pps and the VCXO ? CPU's DAC's Some software, including a sigma delta DAC, the effect of which is no different, in principle, than the filtering etc required by any of your phase detector implementations. The 1 bit phase error samples are processed in software (or hardware depending on one's inclinations, expertise, etc) in a similar way that samples from an N (1) phase detector samples are, to produce a digital output for a DAC which drives the OCXO EFC input. The only difference is that a sigma delta DAC is used instead of a conventional DAC. if so how does your complexity arguments still apply ? The interpretation of complexity depends on ones background and experience. The originator of the thread indicated that they had some microprocessor software experience. Luis Cupido I was trying to tailor the design to the stated strengths of the originator of the thread. If one is trying to squeeze the ultimate in performance when using a GPS receiver to discipline an OCXO, then carrier phase measurements potentially offer much higher performance than can be achieved by using the PPS output of a typical GPS timing receiver. However only a few commercially available GPS receivers are suitable for this application. The GPS receiver oscillators all have to be phase locked to the OCXO being disciplined. This approach has been used in at least one commercially available GPSDOCXO. In principle a GPS receiver has all the required measurement hardware, so all that is required are suitable algorithms implemented in either software running on a DSP, microprocessor, etc, or implemented in hardware (CPLD etc). Bruce ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Scott Scott Burris wrote: Bruce Griffiths wrote: As far as I know Dallas/Maxim appears to be the only source of suitable affordable programmable delay chips for this particular application. In principle one could use a tapped chain of gates in a CPLD, however continuous calibration of the delay is required (a delay locked loop controlling the gate propagation delay by adjusting its power supply voltage to compensate for the effect of temperature variations is one technique). However unless the Dallas chips become hard to obtain its probably best to leave this as a backup option. What about sending the 1PPS signal through a number of HC family gates and using a mux to select a tap -- is that better than using a CPLD? Hmm, probably the delay varies too much from manufacturer to manufacturer to make this work reliably. Probably temperature sensitive too. All of the above, however the major problems are that the individual gate delay is too long and the designing a suitable multiplexer isnt easy. I dont think that cascading 30 or more 1ns delay gates all in different packages is going to work that well. CPLDs have the advantage that to a first approximation all the gate delays are identical. However you have to force the configuration to interconnect them appropriately software so as not to spoil the performance. What kind of delay characteristics are needed? I see some other delay lines with 100ps steps available, see: With an M12+T you need a minimum variable delay range of about 20ns or so with a step size, accuracy and stability of better than 1ns (resolution of sawtooth correction message) to avoid degrading performance. Tom Clark suggested that the DS1020-15 with 150ps resolution is OK for this receiver, however it needs to be calibrated over the delay range used. Other receivers (particularly older ones) will need larger delay ranges. The required delay range is around 0.5 to 1x the receiver timing clock period for the Motorola receivers. Autocalibration techniques can be used to track the effects of temperature and aging. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=408-1127-ND and put that through a mux? In principle this would work, the devil lies in the detail of the mux design. The mux delay needs to be independent of the selected tap. The delay range provided by one of these devices is too small. As a fallback option I have produced a draft schematic of a ramp style delay generator with a resolution of 100ps and a range of 400ns or so. The extended range allows calibration against a 10MHz OCXO derived clock and should allow it to be used with most of the older Motorola Timing receivers that provide sawtooth correction data. Such calibrations can be interleaved between successive PPS pulses. A 12 bit resolution DAC with a settling time (to 0.01%) of around 100millisec or so is required for this DAC. It may be feasible to use a PWM DAC for this. Looks like some of the DS1020's are available through Maxim's e-commerce site, but some have a 15 week lead time, depending on the particular model. What processor are you intending to use to decipher the sawtooth correction messages from the GPS timing receiver? You could use an inexpensive microprocessor dedicated to this simple task. Another microprocessor can be used to discipline the OCXO. Depending on your experience, this can be easier than using a single microprocessor to do everything. I have experience with PICs, Atmel AVRs, and various ARM flavors, and limited experience with SOC processors in Xilinx FPGAs (Picoblaze and the like). PICs and AVRs are cheap, so no problem dedicating one to this task. Anyone have a list of GPS units which provide sawtooth correction data? I have a few flavors of Motorola products and a Trimble Lassen IQ laying around. They all provide 1PPS signals, but I bet some don't have the necessary features. M12MT, M12+T, Trimble Resolution-T all provide sawtooth correction data. Scott Bruce ___ 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] SVN37 offline
I'm sure you all noticed, SVN37 (PRN07) went offline today. I tracked it yesterday afternoon, but it is gone today: http://www.mock.com/test/z3801a/ Looks like it might be gone for good, now we only have 29 GPS satellites online... ftp://tycho.usno.navy.mil/pub/gps/gps.txt jeff ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Scott Data delay devices (http://www.datadelay.com) also do programmable delay lines their minimum order is $US75 which isnt too bad particularly if more than one sawtooth corrector is to be built. They even do ECL programmable delays as do Micrel (http://www.micrel.com). However these ECL programmable delay devices dont have enough range for this application. If you solve the multiplexer problem and use embedded calibration you could use circuit board traces to implement the delay line sections, however a lot of PCB real estate would be required. Such delays also have significant tempcos when using fibre glass PCB substrates. Bruce ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
On Dec 12, 2007 2:32 AM, Bruce Griffiths [EMAIL PROTECTED] wrote: Michael The analog circuitry for a sigma-delta DAC is attached. The input is optically isolated using a high speed low jitter CMOS optocoupler (Avago produce an equivalent device) to break low frequency ground loops. I was wondering if the Avago HCPL-9000 or Analog's ADUM1100 iCoupler would be suitable alternatives to the HCPL-7100. Similarly an RF transformer should be used to couple the OCXO output to the Digital board breaking another potential low frequency ground loop. For the RF transformer I am considering a Coilcraft WB1-6(S)L transformer to decouple the OCXO output. http://www.coilcraft.com/wb_th.cfm I want to do some more reading, but I think I'm might have some questions about DAC input data (from the microprocessor). Would there be any problems, or benefits to using AHC versus AC logic family flipflops and the inverting Schmitt triggers? In regards to the sawtooth correction, I am undecided. If I understand correctly, even without not addressing it there should be an improvement over existing public designs (Shera, Miller). If I remember correctly, you were keen on a software/firmware based sawtooth approach, if so that might be more flexible and cheaper than fiddling with a uncalibrated DS1020 delay line. Thank you, Michael ___ 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] SVN37 offline
On Dec 12, 2007 8:55 PM, Jeff Mock [EMAIL PROTECTED] wrote: I'm sure you all noticed, SVN37 (PRN07) went offline today. I tracked it yesterday afternoon, but it is gone today: http://www.mock.com/test/z3801a/ Looks like it might be gone for good, now we only have 29 GPS satellites online... ftp://tycho.usno.navy.mil/pub/gps/gps.txt There's a chance it'll come back, though it's SVN suggests that maybe it's getting old and tired. It did go active 14.5 yrs ago... maybe they just want cut the springs, bolt a wing on the back and add some racing stripes? NANU 2007010 - SVN27 offline 1hr NANU 2007166 - SVN32 offline 45min NANU 2007123 - SVN41 offline 5hr NANU 2007115 - SVN32 offline 3hr NANU 2007111 - SVN40 offline 3.5wk does any of this correlate with some orbital maneuvering? CK -- GDB has a 'break' feature; why doesn't it have 'fix' too? ___ 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] is there a best bet advanced hobbyist buildable GPSDOdesign?
Michael michael taylor wrote: On Dec 12, 2007 2:32 AM, Bruce Griffiths [EMAIL PROTECTED] wrote: Michael The analog circuitry for a sigma-delta DAC is attached. The input is optically isolated using a high speed low jitter CMOS optocoupler (Avago produce an equivalent device) to break low frequency ground loops. I was wondering if the Avago HCPL-9000 or Analog's ADUM1100 iCoupler would be suitable alternatives to the HCPL-7100. Check the jitter, no jitter specs given for the iCouplers. You may have to measure it on a sample. The HCPL9000 should be fine but measure the jitter. Circuit is actually reasonably tolerant to jitter as the low pass filter averages such effects over many cycles. If jitter proves a problem then if the micro or other logic generating the sigma delta DAC bit-stream is clocked by the OCXO a D flipflop can be used to retime the bitstream after the optocoupler/isolator reducing the bit stream jitter to a few tens of picoseconds or so. Similarly an RF transformer should be used to couple the OCXO output to the Digital board breaking another potential low frequency ground loop. For the RF transformer I am considering a Coilcraft WB1-6(S)L transformer to decouple the OCXO output. http://www.coilcraft.com/wb_th.cfm Probably OK although there appear to be no VSWR specs for these. I want to do some more reading, but I think I'm might have some questions about DAC input data (from the microprocessor). Would there be any problems, or benefits to using AHC versus AC logic family flipflops and the inverting Schmitt triggers? Whilst HC logic performance is adequate there is probably not too much harm in using AHC or even AC as long as you use a ground plane together with suitable layout techniques. Metastability rates would go down by a large factor however the rate with HC logic should be well below once every 1E10 years. In regards to the sawtooth correction, I am undecided. If I understand correctly, even without not addressing it there should be an improvement over existing public designs (Shera, Miller). If I remember correctly, you were keen on a software/firmware based sawtooth approach, if so that might be more flexible and cheaper than fiddling with a uncalibrated DS1020 delay line. Depends on the entire system cost a single chip programmable delay plus a D flipflop and little else should be cheaper than most high resolution phase detector approaches. As long as one can calibrate the DS1020 to improve its performance over the datasheet specs. If it is sufficient to do this once (using a 5370 or equivalent) then the cost may be lower. There are a lot of legacy devices/systems in use that actually require a low jitter PPS pulse. Most phase detectors with resolution, stability and accuracy better than 1ns (needs to be better than 500ps or so avoid significantly degrading the quality of the correction) also require calibration unless one has a suitable (2??) GHz clock (or equivalent) locked to the OCXO being disciplined. 1ns accuracy and stability are perhaps easier to achieve when using a sampled quadrature pair sine wave interpolator but even this requires significant support logic to facilitate measuring harmonic content , quadrature error etc. Thank you, Michael Bruce ___ 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.
