Re: [time-nuts] GPSDO control system
Howdy Charles, Could you tell us more about the PLL, what sort of phase comparator, filters and so forth. I'd be keen to duplicate and test your configuration. Thanks, david David wrote: How do you lock your OCXO to the PRS10? I just use a 1:1 PLL. Some will argue that phase locking two oscillators running at the same frequency is not optimal, but I have found that it can work very well. YMMV. Perhaps locking a 100 MHz OCXO to the PRS10 and dividing its output down to 10 MHz could yield better results (and perhaps not) -- but I have no desire to start collecting 100 MHz OCXOs and culling them to find the best one, so that hypothesis is left for someone else to investigate. 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.
Re: [time-nuts] GPSDO control system
Does anybody have data on the drift of Rs or Cs? Rule of thumb: ... Ah, thanks. But by Rs and Cs I meant plural or R/resistor and C/capacitor. I know they change a lot with temperature, but how much do they drift if the temperature is constant? -- 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] GPSDO control system
David wrote: How do you lock your OCXO to the PRS10? I just use a 1:1 PLL. Some will argue that phase locking two oscillators running at the same frequency is not optimal, but I have found that it can work very well. YMMV. Perhaps locking a 100 MHz OCXO to the PRS10 and dividing its output down to 10 MHz could yield better results (and perhaps not) -- but I have no desire to start collecting 100 MHz OCXOs and culling them to find the best one, so that hypothesis is left for someone else to investigate. 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.
Re: [time-nuts] GPSDO control system
Hi Which R’s and C’s did you buy? There are a *lot* of different types and they each have their issues. A very common issue is - “they came from the store”. Any ability to trace them back to a manufacturer and a process has been lost. Bob On Mar 24, 2014, at 2:29 AM, Hal Murray hmur...@megapathdsl.net wrote: Does anybody have data on the drift of Rs or Cs? Rule of thumb: ... Ah, thanks. But by Rs and Cs I meant plural or R/resistor and C/capacitor. I know they change a lot with temperature, but how much do they drift if the temperature is constant? -- 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] GPSDO control system
Bill wrote: 1. The difficulty with disciplining a local oscillator to a GPS signal is due to variations in the received GPS signal and the LO. I'm not sure I'd call that the difficulty -- it is the task of a GPSDO to discipline the local oscillator *at time scales where the GPS is better than the oscillator*. The oscillator wanders, and the GPS signal has noise and jitter. The oscillator controls stability at small to medium tau, so improvements there require a better oscillator (nothing you do on the GPS side is going to improve overall stability below tau = 100 seconds or so). If you have an exceptionally stable oscillator, this will be true out to tau = 1000 or even beyond. 3. The gain of the system, in degrees of phase angle at 10 MHz (or higher) per microvolt of control signal, is fairly constant in a controlled environment. The gain function is a free parameter -- it can have pretty much any characteristic you desire, if you are sufficiently creative to realize it. In practice, of course, it will be constrained by the criteria for stability. 4. The power supply for the device providing the control signal cannot be regulated to the accuracy required of the system, and so is a source of variance. The control amplifier should have considerable PSRR, so this should not be a material source of error. The reference for any DAC in the system may contribute error. But that is all inside the control loop, which is driven by a phase comparator of one sort or another. Ultimately, the errors in the inputs (oscillator and GPS) and the phase comparator should dominate the overall performance (if not, you have left something on the table). 5. The principle source of environmental variation is temperature. Humidity and barometric pressure are not significant. This may not be true of the received GPS signal due to atmospheric variations. You will have to test the parts you propose to use to see if they are affected by humidity or barometric pressure. Some researchers have reported sensitivity to one or both for crystal oscillators and voltage references, among other parts. Except for the oscillator, GPS, and phase comparator, that is all inside the control loop. 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.
Re: [time-nuts] GPSDO control system
Hi The real answer is always “that depends”. 1) How much does the sensitivity of your OCXO change with a change in EFC? 1.4:1, 2:1, 4:1 …. (slope sensitivity not % linearity) 2) How quiet is your DAC compared to your OCXO? 3) How quiet is your reference compared to your OCXO? 4) How much do the DAC, reference, op-amps, resistors, capacitors, … drift with time? 5) How much test time is enough? (hours, days, weeks ,…..) 6) How good is the survey on your GPS this time? 7) How much does your room temperature impact your OCXO when you do this or that? 8) Is your room temperature representative of the real world? (is mine like yours?) 9) Do you intend this gizmo to work over a temperature range? Did you test that range? 10) Are you trying for best frequency or best time? Is your definition of time “GPS local time”? 11) Are there voltage drops on your real board? Do they change with anything? (or everything ?) 12) Does your controller generate spurs inside the control loop and modulate the output with them when tuned to an offset of x.xx Hz? 13) How do things respond to load changes or supply voltage changes? 14) Are the parts (OCXO, reference, dac, op amps …) responses to temperature, load, supply, tip, tune, linear / immediate or do they have artifacts that extend out over longer time periods? This is by no means a complete list. A lot of common GPS issues are notably absent. However, I’ve seen designs fail or fall short for problems related to every item on that list. Can you put this all in a model - sure. Did you put all this in the model .. .. Bob On Mar 23, 2014, at 5:06 AM, Bill Hawkins b...@iaxs.net wrote: An idea is struggling to take shape in my fevered brain. I'd like to check some foundation assumptions. 1. The difficulty with disciplining a local oscillator to a GPS signal is due to variations in the received GPS signal and the LO. 2. The variations occur slowly, as crystal aging, and quickly - perhaps sawtooth or crystal crack propagation - and maybe something in between. 3. The gain of the system, in degrees of phase angle at 10 MHz (or higher) per microvolt of control signal, is fairly constant in a controlled environment. 4. The power supply for the device providing the control signal cannot be regulated to the accuracy required of the system, and so is a source of variance. (Does anyone put the voltage reference device in the oven with the crystal?) 5. The principle source of environmental variation is temperature. Humidity and barometric pressure are not significant. This may not be true of the received GPS signal due to atmospheric variations. 6. A digital computational device is available to calculate the control signal from various measurements and previous values. 7. There are no supernatural forces at work, such as the experimenter mentally influencing the results. :-) That's a start . . . Thanks for any replies. Bill Hawkins ___ 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] GPSDO control system
On 23/03/14 14:02, Bob Camp wrote: Hi The real answer is always “that depends”. 1) How much does the sensitivity of your OCXO change with a change in EFC? 1.4:1, 2:1, 4:1 …. (slope sensitivity not % linearity) 2) How quiet is your DAC compared to your OCXO? 3) How quiet is your reference compared to your OCXO? 4) How much do the DAC, reference, op-amps, resistors, capacitors, … drift with time? 5) How much test time is enough? (hours, days, weeks ,…..) 6) How good is the survey on your GPS this time? 7) How much does your room temperature impact your OCXO when you do this or that? 8) Is your room temperature representative of the real world? (is mine like yours?) 9) Do you intend this gizmo to work over a temperature range? Did you test that range? 10) Are you trying for best frequency or best time? Is your definition of time “GPS local time”? 11) Are there voltage drops on your real board? Do they change with anything? (or everything ?) 12) Does your controller generate spurs inside the control loop and modulate the output with them when tuned to an offset of x.xx Hz? 13) How do things respond to load changes or supply voltage changes? 14) Are the parts (OCXO, reference, dac, op amps …) responses to temperature, load, supply, tip, tune, linear / immediate or do they have artifacts that extend out over longer time periods? This is by no means a complete list. A lot of common GPS issues are notably absent. However, I’ve seen designs fail or fall short for problems related to every item on that list. Can you put this all in a model - sure. Did you put all this in the model .. .. 15) As the AC shifts voltage, how does that change the power consumption in the PSU and hence change the heating in or near your box? 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] GPSDO control system
Hi One thing that should be noted. Some of this stuff has zero impact at long tau. Some of it only has an impact at long tau. It might be easier to split a model into long and short versions to deal with this stuff. Getting the data is the next step. You can find app notes on some voltage references that show things like hysteresis, warmup and retrace. Getting the same data on DAC’s or resistors is a bit tough. If you use ceramic caps, you can find non-linear model data on them (sort of). Even with the data, turning it into something that fits in a model isn’t easy at all. When you find that your 2 ppm reference has 40 ppm of hysteresis, including that in the model might move up your list a bit…. Bob On Mar 23, 2014, at 10:02 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 23/03/14 14:02, Bob Camp wrote: Hi The real answer is always “that depends”. 1) How much does the sensitivity of your OCXO change with a change in EFC? 1.4:1, 2:1, 4:1 …. (slope sensitivity not % linearity) 2) How quiet is your DAC compared to your OCXO? 3) How quiet is your reference compared to your OCXO? 4) How much do the DAC, reference, op-amps, resistors, capacitors, … drift with time? 5) How much test time is enough? (hours, days, weeks ,…..) 6) How good is the survey on your GPS this time? 7) How much does your room temperature impact your OCXO when you do this or that? 8) Is your room temperature representative of the real world? (is mine like yours?) 9) Do you intend this gizmo to work over a temperature range? Did you test that range? 10) Are you trying for best frequency or best time? Is your definition of time “GPS local time”? 11) Are there voltage drops on your real board? Do they change with anything? (or everything ?) 12) Does your controller generate spurs inside the control loop and modulate the output with them when tuned to an offset of x.xx Hz? 13) How do things respond to load changes or supply voltage changes? 14) Are the parts (OCXO, reference, dac, op amps …) responses to temperature, load, supply, tip, tune, linear / immediate or do they have artifacts that extend out over longer time periods? This is by no means a complete list. A lot of common GPS issues are notably absent. However, I’ve seen designs fail or fall short for problems related to every item on that list. Can you put this all in a model - sure. Did you put all this in the model .. .. 15) As the AC shifts voltage, how does that change the power consumption in the PSU and hence change the heating in or near your box? 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] GPSDO control system
4) How much do the DAC, reference, op-amps, resistors, capacitors, drift with time? Assuming constant temperature and supply voltage... What is the time scale for parts drifting? Is it very low frequency so well within the loop bandwidth or is it jumps that will be hard to filter out? What happens if temperature or voltage is not constant? Are the changes reasonably linear with temperature/voltage? -- 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] GPSDO control system
Hi There are many issues when it comes to a GPSO. But what has to be first discussed what is it one wants to accomplish. Last year when we worked on the latest Shera GPSDO we always got better than 1E-11 with a unit lying on the bench with no enclosure or thermal management. Chasing elusive 1 E-13 and better, allow me to make a couple of comments. In order to get there, the total system has to be under review. Since I know nothing about writing programs I leave that to smarter people but be clear software and code will not do it by it self. The most critical part is the thermal management of the OCXO or Rb and if analog control is used the DAC.and if used its output amp. We are controlling the back plate of the M100 and FRK to within 0.01 C and the front 0.1 C. The DAC board and the temperature controller are on the front, Voltage regulators on the back. After extensive testing the LTC1655 is our preferred choice. Take a close look specs are great for this application and most important solderable. There are better DAC's out there but very expensive and I am not able to solder. 18 bits would be nicer but 16 bits are for Rb's usable. The DAC part has to have its own ground plane because ground loops can create noise and voltage changes it has to be tied as close and separate to the OCXO or Rb. No opto Isolation necessary as long as the controller and DAC are in the same box, sharing the same system ground. Input to the DAC can handle wide ground variations. Took me years to find that out. Absolute must how ever is opto isolation between GPS, controller and PC, again found out the hard way. The other part I like to touch on is the GPS input section. I am not a time nut but a frequency nut, but there has been so much talk in the past and more recently about sawtooth. I am disappointed but not surprised that no one has stepped up and offered a solution. The site has deteriorated to a lot of talk very little action. Right now there are still affordable and solderable DS1023's out there. Combined with a 12F629 or 12F1840 a sawtooth correction is possible for much less than $20. I bought last year four DIP and 10 in SOIC DS's average price below $ 5! Even though I had a very bad experience once with a Dutch so called time nut I am willing to make the following offer. For the right person I make a board, PIC and DS1023 available. Maybe I just missed it but I do not think that there is something out there readily available. Bert Kehren In a message dated 3/23/2014 9:02:59 A.M. Eastern Daylight Time, li...@rtty.us writes: Hi The real answer is always “that depends”. 1) How much does the sensitivity of your OCXO change with a change in EFC? 1.4:1, 2:1, 4:1 …. (slope sensitivity not % linearity) 2) How quiet is your DAC compared to your OCXO? 3) How quiet is your reference compared to your OCXO? 4) How much do the DAC, reference, op-amps, resistors, capacitors, … drift with time? 5) How much test time is enough? (hours, days, weeks ,…..) 6) How good is the survey on your GPS this time? 7) How much does your room temperature impact your OCXO when you do this or that? 8) Is your room temperature representative of the real world? (is mine like yours?) 9) Do you intend this gizmo to work over a temperature range? Did you test that range? 10) Are you trying for best frequency or best time? Is your definition of time “GPS local time”? 11) Are there voltage drops on your real board? Do they change with anything? (or everything ?) 12) Does your controller generate spurs inside the control loop and modulate the output with them when tuned to an offset of x.xx Hz? 13) How do things respond to load changes or supply voltage changes? 14) Are the parts (OCXO, reference, dac, op amps …) responses to temperature, load, supply, tip, tune, linear / immediate or do they have artifacts that extend out over longer time periods? This is by no means a complete list. A lot of common GPS issues are notably absent. However, I’ve seen designs fail or fall short for problems related to every item on that list. Can you put this all in a model - sure. Did you put all this in the model .. .. Bob On Mar 23, 2014, at 5:06 AM, Bill Hawkins b...@iaxs.net wrote: An idea is struggling to take shape in my fevered brain. I'd like to check some foundation assumptions. 1. The difficulty with disciplining a local oscillator to a GPS signal is due to variations in the received GPS signal and the LO. 2. The variations occur slowly, as crystal aging, and quickly - perhaps sawtooth or crystal crack propagation - and maybe something in between. 3. The gain of the system, in degrees of phase angle at 10 MHz (or higher) per microvolt of control signal, is fairly constant in a controlled environment. 4. The power supply for the device providing the control signal cannot be
Re: [time-nuts] GPSDO control system
Hi If you have a source of “noise” that is not in your model *and* it’s significant, then your model will not predict the outcome. That’s true if it’s in or if it’s outside the loop bandwidth. Bob On Mar 23, 2014, at 2:27 PM, Hal Murray hmur...@megapathdsl.net wrote: 4) How much do the DAC, reference, op-amps, resistors, capacitors, drift with time? Assuming constant temperature and supply voltage... What is the time scale for parts drifting? Is it very low frequency so well within the loop bandwidth or is it jumps that will be hard to filter out? What happens if temperature or voltage is not constant? Are the changes reasonably linear with temperature/voltage? -- 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] GPSDO control system
I'm working on a GPSDO but with different goals. I want mine to be 1) very low cost, under $50 for everything if I can 2) No PCB required. 3) very easy to replicate by a first time builder 4) Easy to understand. The parts count is very low, no exotic parts and the software written very clearly so the code reads like the tutorial for a beginner. I started with Lars' Arduino based design and I've making slight mods. But shipping from China takes a month and I'm waiting on parts.I expect only 1E-11 level performance The next one I build I want to be different. I don't need yet another copy of an old design. 1) Can I combine two oscillator technologies to get the best of both? Perhaps phase lock an OCXO to a Rb and then discipline the Rb's frequency. 2) is there some good way to control the temperature of the entire assembly? Perhaps dunk the entire thing into a container of transformer oil? Or use thermal epoxy to connect all the critical parts to ONE common heat sink and then keep that at constant temperature. First I need some way to measure temperature very accurately. 3) are 10MHz crystals the most stable ones? I bet there is a sweat spot frequency that is better. Would 50MHz or 5Mhz be better? 4) why use a PPS as the communications link from GPS to GPSDO? Can I find a way to move the OXCO into the guts of a GPS receiver. That may mean I have to build a SDR based GPS receiver. But first the simple one. I'll post progress reports and photos On Sun, Mar 23, 2014 at 11:32 AM, ewkeh...@aol.com wrote: Hi There are many issues when it comes to a GPSO. But what has to be first discussed what is it one wants to accomplish. Last year when we worked on the latest Shera GPSDO we always got better than 1E-11 with a unit lying on the bench with no enclosure or thermal management. Chasing elusive 1 E-13 and better, allow me to make a couple of comments. In order to get there, the total system has to be under review. Since I know nothing about writing programs I leave that to smarter people but be clear software and code will not do it by it self. The most critical part is the thermal management of the OCXO or Rb and if analog control is used the DAC.and if used its output amp. We are controlling the back plate of the M100 and FRK to within 0.01 C and the front 0.1 C. The DAC board and the temperature controller are on the front, Voltage regulators on the back. After extensive testing the LTC1655 is our preferred choice. Take a close look specs are great for this application and most important solderable. There are better DAC's out there but very expensive and I am not able to solder. 18 bits would be nicer but 16 bits are for Rb's usable. The DAC part has to have its own ground plane because ground loops can create noise and voltage changes it has to be tied as close and separate to the OCXO or Rb. No opto Isolation necessary as long as the controller and DAC are in the same box, sharing the same system ground. Input to the DAC can handle wide ground variations. Took me years to find that out. Absolute must how ever is opto isolation between GPS, controller and PC, again found out the hard way. The other part I like to touch on is the GPS input section. I am not a time nut but a frequency nut, but there has been so much talk in the past and more recently about sawtooth. I am disappointed but not surprised that no one has stepped up and offered a solution. The site has deteriorated to a lot of talk very little action. Right now there are still affordable and solderable DS1023's out there. Combined with a 12F629 or 12F1840 a sawtooth correction is possible for much less than $20. I bought last year four DIP and 10 in SOIC DS's average price below $ 5! Even though I had a very bad experience once with a Dutch so called time nut I am willing to make the following offer. For the right person I make a board, PIC and DS1023 available. Maybe I just missed it but I do not think that there is something out there readily available. Bert Kehren In a message dated 3/23/2014 9:02:59 A.M. Eastern Daylight Time, li...@rtty.us writes: Hi The real answer is always that depends. 1) How much does the sensitivity of your OCXO change with a change in EFC? 1.4:1, 2:1, 4:1 (slope sensitivity not % linearity) 2) How quiet is your DAC compared to your OCXO? 3) How quiet is your reference compared to your OCXO? 4) How much do the DAC, reference, op-amps, resistors, capacitors, ... drift with time? 5) How much test time is enough? (hours, days, weeks ,.) 6) How good is the survey on your GPS this time? 7) How much does your room temperature impact your OCXO when you do this or that? 8) Is your room temperature representative of the real world? (is mine like yours?) 9) Do you intend this gizmo to work over a temperature range? Did you test that range? 10) Are you trying for best frequency or
Re: [time-nuts] GPSDO control system
You are nine days too early. :) Tom - Original Message - From: Chris Albertson albertson.ch...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, March 23, 2014 5:26 PM Subject: Re: [time-nuts] GPSDO control system I'm working on a GPSDO but with different goals. I want mine to be 1) very low cost, under $50 for everything if I can 2) No PCB required. 3) very easy to replicate by a first time builder 4) Easy to understand. The parts count is very low, no exotic parts and the software written very clearly so the code reads like the tutorial for a beginner. I started with Lars' Arduino based design and I've making slight mods. But shipping from China takes a month and I'm waiting on parts.I expect only 1E-11 level performance The next one I build I want to be different. I don't need yet another copy of an old design. 1) Can I combine two oscillator technologies to get the best of both? Perhaps phase lock an OCXO to a Rb and then discipline the Rb's frequency. 2) is there some good way to control the temperature of the entire assembly? Perhaps dunk the entire thing into a container of transformer oil? Or use thermal epoxy to connect all the critical parts to ONE common heat sink and then keep that at constant temperature. First I need some way to measure temperature very accurately. 3) are 10MHz crystals the most stable ones? I bet there is a sweat spot frequency that is better. Would 50MHz or 5Mhz be better? 4) why use a PPS as the communications link from GPS to GPSDO? Can I find a way to move the OXCO into the guts of a GPS receiver. That may mean I have to build a SDR based GPS receiver. But first the simple one. I'll post progress reports and photos On Sun, Mar 23, 2014 at 11:32 AM, ewkeh...@aol.com wrote: Hi There are many issues when it comes to a GPSO. But what has to be first discussed what is it one wants to accomplish. Last year when we worked on the latest Shera GPSDO we always got better than 1E-11 with a unit lying on the bench with no enclosure or thermal management. Chasing elusive 1 E-13 and better, allow me to make a couple of comments. In order to get there, the total system has to be under review. Since I know nothing about writing programs I leave that to smarter people but be clear software and code will not do it by it self. The most critical part is the thermal management of the OCXO or Rb and if analog control is used the DAC.and if used its output amp. We are controlling the back plate of the M100 and FRK to within 0.01 C and the front 0.1 C. The DAC board and the temperature controller are on the front, Voltage regulators on the back. After extensive testing the LTC1655 is our preferred choice. Take a close look specs are great for this application and most important solderable. There are better DAC's out there but very expensive and I am not able to solder. 18 bits would be nicer but 16 bits are for Rb's usable. The DAC part has to have its own ground plane because ground loops can create noise and voltage changes it has to be tied as close and separate to the OCXO or Rb. No opto Isolation necessary as long as the controller and DAC are in the same box, sharing the same system ground. Input to the DAC can handle wide ground variations. Took me years to find that out. Absolute must how ever is opto isolation between GPS, controller and PC, again found out the hard way. The other part I like to touch on is the GPS input section. I am not a time nut but a frequency nut, but there has been so much talk in the past and more recently about sawtooth. I am disappointed but not surprised that no one has stepped up and offered a solution. The site has deteriorated to a lot of talk very little action. Right now there are still affordable and solderable DS1023's out there. Combined with a 12F629 or 12F1840 a sawtooth correction is possible for much less than $20. I bought last year four DIP and 10 in SOIC DS's average price below $ 5! Even though I had a very bad experience once with a Dutch so called time nut I am willing to make the following offer. For the right person I make a board, PIC and DS1023 available. Maybe I just missed it but I do not think that there is something out there readily available. Bert Kehren In a message dated 3/23/2014 9:02:59 A.M. Eastern Daylight Time, li...@rtty.us writes: Hi The real answer is always that depends. 1) How much does the sensitivity of your OCXO change with a change in EFC? 1.4:1, 2:1, 4:1 (slope sensitivity not % linearity) 2) How quiet is your DAC compared to your OCXO? 3) How quiet is your reference compared to your OCXO? 4) How much do the DAC, reference, op-amps, resistors, capacitors, ... drift with time? 5) How much test time is enough? (hours, days, weeks ,.) 6) How good is the survey on your GPS this time? 7) How much does your room temperature impact your
Re: [time-nuts] GPSDO control system
Chris wrote: 4) why use a PPS as the communications link from GPS to GPSDO? Generally, because that is the only precision timing output you get from a GPS unit. The models with a 10kHz output were prized by the simple GPSDO crowd precisely for the fact that the phase-locked 10kHz signal made the control loop much easier to design (or, made an analog loop *possible* to design). Can I find a way to move the OXCO into the guts of a GPS receiver. I don't know. Can you? That is essentially what the Thunderbolt does, and it brings with it the tremendous advantage that it removes the sawtooth error -- which is why some of us think so highly of that design. But now you are really down and dirty, designing your own GPS receiver. Are you competent (and, if so, willing) to do that? (You are very, very far from a simple GPSDO if you are considering this.) Honestly, I never understood why all timing receivers aren't designed that way. It seems to be such a superior way to do things that I'd have thought the other approaches would have died out once everybody knew about it. Even if Trimble has a patent, I can't imagine it would be that expensive to license. But even Trimble doesn't use it on all of their timing receivers. Anybody know why this scheme hasn't been used more widely? Is there something I'm missing? 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.
Re: [time-nuts] GPSDO control system
li...@rtty.us said: If you have a source of noise that is not in your model *and* its significant, then your model will not predict the outcome. Thats true if its in or if its outside the loop bandwidth. Does anybody have data on the drift of Rs or Cs? In this context, is it significant? I assume it depends on the circuit involved. I'm just looking for the big picture. I expect any drift is lost in the noise if the temperature and such aren't stable. -- 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] GPSDO control system
Hal wrote: Does anybody have data on the drift of Rs or Cs? Tom has some data posted at leapsecond.com (for H-masers, too). John Miles has some at ke5fx.com. John Ackermann has some at febo.com. I encourage you to roam widely over all three sites -- you will be well rewarded. 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.
Re: [time-nuts] GPSDO control system
csteinm...@yandex.com said: Can I find a way to move the OXCO into the guts of a GPS receiver. I don't know. Can you? That is essentially what the Thunderbolt does, and it brings with it the tremendous advantage that it removes the sawtooth error -- which is why some of us think so highly of that design. But now you are really down and dirty, designing your own GPS receiver. Are you competent (and, if so, willing) to do that? (You are very, very far from a simple GPSDO if you are considering this.) I agree that it won't be simple, but it's likely to be within range of many of us, if not now, then soon. The SDR guys are doing lots of great work. I haven't looked at any of the details, but google gets several hits for SDR GPS. It would be interesting to investigate turning the software into timing mode and/or turning that into a GPSDO. -- 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] GPSDO control system
On 24/03/14 00:08, Charles Steinmetz wrote: Chris wrote: 4) why use a PPS as the communications link from GPS to GPSDO? Generally, because that is the only precision timing output you get from a GPS unit. The models with a 10kHz output were prized by the simple GPSDO crowd precisely for the fact that the phase-locked 10kHz signal made the control loop much easier to design (or, made an analog loop *possible* to design). Can I find a way to move the OXCO into the guts of a GPS receiver. I don't know. Can you? That is essentially what the Thunderbolt does, and it brings with it the tremendous advantage that it removes the sawtooth error -- which is why some of us think so highly of that design. But now you are really down and dirty, designing your own GPS receiver. Are you competent (and, if so, willing) to do that? (You are very, very far from a simple GPSDO if you are considering this.) Honestly, I never understood why all timing receivers aren't designed that way. It seems to be such a superior way to do things that I'd have thought the other approaches would have died out once everybody knew about it. Even if Trimble has a patent, I can't imagine it would be that expensive to license. But even Trimble doesn't use it on all of their timing receivers. Anybody know why this scheme hasn't been used more widely? Is there something I'm missing? For the more expensive GPS receivers, they have been using OCXO, some even suspended OCXOs. Also, as an option you can connect an external clock for additional stability, and for some you can steer this clock. Many of the OEM GPS boards is just... el cheapo. So, you need to look beyond those to find other solutions. For a GPS receiver itself, it doesn't need a clock to be sharp on time, as most of them is designed to handle a clock at the wrong rate. What they however do is learn and compensate for phase and frequency errors. Also, the performance of the clock will affect the produced results, and ẃhen doing precision measures of code-phase for L1 and L2, the benefit is certainly there. 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] GPSDO control system
I've lost track now of who it was, but someone asked if there was a better strategy than a GPS disciplined quartz oscillator or a GPS disciplined rubidium. My best standard uses an SRS PRS10 rubidium disciplined by GPS PPS at tau = VERY long ( ~12 hours), using the PRS10's internal PPS locking. The rubidium, in turn, disciplines my best OCXO at tau 300 seconds. So, for tau less than ~300 seconds the stability is determined by the OCXO; for tau greater than ~300 seconds and less than ~12 hours, the stability is determined by the rubidium; and for tau ~12 hours, the stability is determined by GPS. I have found that this works very well. Note that the PRS10's digital PPS PLL has a bewildering array of adjustable parameters. One can easily get lost exploring different combinations. My advice is to keep it as simple as possible. 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.
Re: [time-nuts] GPSDO control system
Rule of thumb: - really good OCXO have frequency drift rates of 1e-10 to 1e-11/day - common Rb have frequency drift rates on the order of 1e-11/month - Cs do not have frequency drift - H-maser drift rates are 1e-15 to 1e-16/day /tvb (i5s) On Mar 23, 2014, at 4:32 PM, Charles Steinmetz csteinm...@yandex.com wrote: Hal wrote: Does anybody have data on the drift of Rs or Cs? Tom has some data posted at leapsecond.com (for H-masers, too). John Miles has some at ke5fx.com. John Ackermann has some at febo.com. I encourage you to roam widely over all three sites -- you will be well rewarded. 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. ___ 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] GPSDO control system
Hi …. and GPS has cyclic issues on a 24 / 48 hour basis …. Bob On Mar 23, 2014, at 8:58 PM, Tom Van Baak (lab) t...@leapsecond.com wrote: Rule of thumb: - really good OCXO have frequency drift rates of 1e-10 to 1e-11/day - common Rb have frequency drift rates on the order of 1e-11/month - Cs do not have frequency drift - H-maser drift rates are 1e-15 to 1e-16/day /tvb (i5s) On Mar 23, 2014, at 4:32 PM, Charles Steinmetz csteinm...@yandex.com wrote: Hal wrote: Does anybody have data on the drift of Rs or Cs? Tom has some data posted at leapsecond.com (for H-masers, too). John Miles has some at ke5fx.com. John Ackermann has some at febo.com. I encourage you to roam widely over all three sites -- you will be well rewarded. 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. ___ 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] GPSDO control system
Hi Charles, How do you lock your OCXO to the PRS10? Thanks, david I've lost track now of who it was, but someone asked if there was a better strategy than a GPS disciplined quartz oscillator or a GPS disciplined rubidium. My best standard uses an SRS PRS10 rubidium disciplined by GPS PPS at tau = VERY long ( ~12 hours), using the PRS10's internal PPS locking. The rubidium, in turn, disciplines my best OCXO at tau 300 seconds. So, for tau less than ~300 seconds the stability is determined by the OCXO; for tau greater than ~300 seconds and less than ~12 hours, the stability is determined by the rubidium; and for tau ~12 hours, the stability is determined by GPS. I have found that this works very well. Note that the PRS10's digital PPS PLL has a bewildering array of adjustable parameters. One can easily get lost exploring different combinations. My advice is to keep it as simple as possible. 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.
