[time-nuts] new gps sat prn30 svn64
I've done the math subtracting both skips and my clock bias's and frequency drifts from sirf msg30 (prn30) that were posted on timenuts earlier this week; 1.3331348485e-006 3.6930953087e-012 my data 1.3294251003e-006 3.6977287551e-012 skips .0037097482e-006 -.0046334464e-012 3.709748ns -4.633446e-015 Skip's gps clock is 3.7 nanosec slower than my gps clock. And our gps internal oscillators differ in frequency by -4.633446e-15. this could be a timenuts first. Gps common mode time and frequency comparison. skip and I are using sirf-4 gps receiver and sirfdemo software ver. 3.87 downloadable from the web. the receiver is a global sat (sirf-4) bu-353s4 mag mount usb gps receiver. ubtained from gps city in las vegas. They have an online store. My first bu353-s4 was purchased from ebay from someone in utah. It had bad sensivity. My holux gr-213 sirf III receiver which has the best sensitivity was from ebay china 5 or 6 years ago.. It has the sbas satellites (old prn sbas sats) hardcoded in firmware and will not receive any current sbas sats.. I believe the holux gr-213 sirf-3 mag mount usb gps are still sold. But must certainly have the new sbas satellites hardcoded correctly ? The holux gr-213 sirf-3 generated rfi so If your a hf ham radio operator you might not want a sirf-3 holux gr-213 receiver. Sincerly Tom. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
https://www.febo.com/pages/gps_pps/ It appears the implementation of the sawtooth error correction severely degrades the performance of the system. There could be many reasons, which is why it is important to nail down as many of the error sources as possible. severely degrades?? How do you reach this conclusion? It looks to me that sawtooth correction gives a 10x *improvement* in that plot. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Tom and Bob, It is not obvious to me that it is easier to simply apply a correction in nS increments with a range as wide as 100nS. How is this done? Using switched delay lines or delay gates? Didier, If you intend to measure the 1PPS there is no need to correct or adjust it prior to measurement. Each second you simply apply the numerical sawtooth correction value to the numerical 1PPS measurement value. This is the pure software solution. Most people who use GPS for timing do it this way -- since they are already employing a sub-ns TIC to compare their standalone lab reference against the GPS tick. The software solution introduces no additional errors. This method also applies to any GPSDO which incorporates a digital TIC. On the other hand, if you intend to improve the accuracy of the 1PPS without measurement, you need a hardware solution instead. The classic approach is to delay, each second, the hardware 1PPS by N + sawtooth correction. You choose N (depends on the GPS receiver) so that the delay is never less than or too near zero. The one-chip solution I found was the Dallas DS1020 and that's what Rick used in his CNS-II product. Maxim (bought Dallas) now has alternative silicon delay lines that do the equivalent. Note the hardware solution is never quite as good as the software solution since there are offset, gain, linearity, and tempco issues with programmable delay lines. But it's usually close enough. Rick measured the difference between the two methods: 0.7 ns rms. See page 27-31 of http://www.cnssys.com/files/tow-time2009.pdf for details and his wonderful graphs. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi, Agree. If you steer so you keep to be off frequency so you have plenty of sawtooth you get better resolution. I've been pondering about maybe write an article to illustrate the effect. Cheers, Magnus On 04/03/14 23:45, Bob Camp wrote: Hi Be careful of what you wish for. One way to “eliminate” the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. The other way is to put the oscillator well off frequency. That way you have lots of sawtooth action. There are lots of ways to get an oscillator off frequency …. Bob On Mar 4, 2014, at 12:00 PM, Didier Juges shali...@gmail.com wrote: What would be more interesting would be to adjust the temperature of the GPS receiver's oscillator to eliminate the hanging bridges altogether, kind of like Trimble does with the Thunderbolt, except that they do it directly instead of indirectly. That may require to characterize the crystal oscillator to find out if it has an appropriate control range over temperature. Didier KO4BB On March 3, 2014 6:51:54 PM CST, Charles Steinmetz csteinm...@yandex.com wrote: Chris wrote: If do have an external frequency reference then the crystal itself makes a good thermometer. So why not use THAT thermometer to control the heat added by the resister. Such a system would respond to changes in ambient temperature by adjusting the power in the resister. We don't even have to care if the crystal's temp-co is nonlinear because we are using a very small temperature range, so small it looks linear. I'll build it. Can you or anyone else subject a simple XCO schematic? Hopefully SIMPLE. What I need is a design that can be pulled down a few PPM so that I can raise it back with a bit of heat. I will have to be kept at a temperer above the hottest it will ever get inside the house, maybe 100F. See below or attached (hopefully). L and C are chosen to resonate at the crystal frequency with XC and XL in the general vicinity of 100 ohms to 1k ohms. What you are proposing is a disciplined oscillator using the oven setpoint as the control input. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi, You still get hanging bridges, but smaller in amplitude and for the same oscillator stability much more short-lived. Cheers, Magnus On 06/03/14 00:03, Bob Camp wrote: Hi If you are going to decode and use the sawtooth data out of the receiver, there’s no need to eliminate the hanging bridges. The sawtooth data does that for you already. Put another way, heating the receiver is *harder* than just using the decoded data…. Bob On Mar 5, 2014, at 9:53 AM, Mike M timen...@binsamp.e4ward.com wrote: Bob Camp wrote: Hi Be careful of what you wish for. One way to eliminate the hanging bridge is to have the oscillator exactly on frequency. That sounds fine. The problem is that you are always in the middle of a bridge. Bob That's fine. Just set the oscillator to keep the bridge in the middle of the range. It should be possible to detect the correct frequency and phase by monitoring the sawtooth correction data from the GPS. Now you have eliminated the sawtooth error and no longer have to add correction for it. This will eliminate the quantization error in the sawtooth correction data since it is no longer needed. If the 1pps loop is properly designed, it should help the loop track the 1pps signal more accurately. Mike ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Another atomic clock question
Hi In modern GPS modules the sawtooth error is no longer truncated at the 1 ns level. The have been giving you far more resolution than that for 10 years now. The resolution is not just useless bits. If you compare the result to a cesium standard they do improve the GPS. Bob On Mar 6, 2014, at 1:30 AM, m...@febo.com wrote: Wow! One post and I've got the two top heavyweights against me! Let me introduce myself. I am a retired electronics engineer with over 50 years of experience in instrumentation and metrology. Here is my patent list: http://www.pst.netii.net/patents.htm Among the achievements listed, I claim credit for the first disclosure of the now universal dual-d phase-frequency detector, and for the technique called Phase Margin Analysis as applied to hard disk bdrive it error analysis. The technology has evolved tremendously since the 1970's, but this was the first to show that rapid bit error analysis was possible. The internet would not be possible without this basic technique, since it would not be possible to manufacture hard disks fast enough. Another significant invention is Binary Sampling. I will talk more about this later, but some information is on my web site at http://www.pst.netii.net/sampler/index.htm also starting on page 6 of http://www.pst.netii.net/pdfs/tdrpaper.pdf One of the significant advantages of the Binary Sampler is the elimination of Gaussian and Impulse noise. Unlike conventional diode bridge samplers, the performance improves as the frequency increases. After working with the Binary Sampler, I am always dismayed to view the noisy graphs presented in time-nuts and other forums. The noise is hiding the interesting stuff and making it virtually impossible to understand what is actually going on. I Think the Binary Sampler can do a lot to help unravel the issues. I now intersperse replies: Hi( While you see a lot of pretty plots in GPS spec sheets showing clean looking sawtooth sort of offsets marching down the page, that?s not what I see on a real receiver. The real data, even compared to a 5071A is much more random. It will indeed ?hang?, but it also will reverse far more often than the pretty data sheets suggest. A simple model would be to add the sawtooth to some sort of random process. The sawtooth comes from the TCXO, the random looking stuff comes from the GPS solution. The oscillator in most timing modules is one form or another of a TCXO. Often they have digital compensation (one way or another). Their frequency versus temperature curves are not the simple third order curve you would expect from a bare crystal. They have a much higher order frequency versus temperature curve (6th, 8th ?). That makes even the simple ?frequency goes down when temp goes up? decision pretty tough. If they are doing some sort of auto correction TCXO based on the GPS it would get even more crazy. In that case the curve would be changing real time. Since the sawtooth changes multiple ?runs? per minute in a room that holds 2C / 30 minutes, you could guess that a control of 0.01C would be needed to have any luck steering the oscillator. It?s nowhere near that simple, so that?s not even up to the ?wild guess? level of confidence. If it?s close, that?s not going to be very easy all by it?s self. A double loop control is likely to be needed. Combine the random jitter with the (possibly) tough temperature control problem, and frequency reversals - this is a real can of worms. ??? Way lots easier approach: 1) You already need a CPU to set up the GPS, read the sawtooth data stream and do a control loop. It?s free / same with either approach. 2) Rip a VCTCXO out of something (or buy one cheap). 3) PWM control the TCXO, use it as your CPU clock 4) Generate a PPS with a timer output on the CPU. 5) Do a cheap / simple / easy TDC on the GPS pps, it will cost less that what ever was going to drive the heater. Now you have a GPSDO with a much lower jitter PPS output. You need to write from scratch code for the CPU either way. The code for the GPSDO is probably simpler than the temperature control code. It?s certainly no more difficult. This way you have an output at what ever the TCXO frequency is for ?other stuff?. Bob Thanks, Bob. I don't propose using temperature to control the GPS clock. I plan to use a AD9912 DDS (1GHz 48Bit 4uHz 0.19ps $59@Newark.) On Mar 5, 2014, at 6:48 PM, Tom Van Baak t...@leapsecond.com wrote: I agree with Bob. For casual use, hanging bridges are not really a problem, statistically speaking -- so don't worry. Yes, you can apply various techniques to reduce/eliminate the rare effect: forced temperature change, forced Vcc change, 2 or 3 or more shared-antenna receivers,
Re: [time-nuts] Another atomic clock question
To the Mike that posted: http://www.pst.netii.net/patents.htm - I tried going to your site - can't reach it. Is the site operational? I wanted to take a look at your patents. Thanks, John Westmoreland On Thu, Mar 6, 2014 at 2:40 PM, Bob Camp li...@rtty.us wrote: Hi In modern GPS modules the sawtooth error is no longer truncated at the 1 ns level. The have been giving you far more resolution than that for 10 years now. The resolution is not just useless bits. If you compare the result to a cesium standard they do improve the GPS. Bob On Mar 6, 2014, at 1:30 AM, m...@febo.com wrote: Wow! One post and I've got the two top heavyweights against me! Let me introduce myself. I am a retired electronics engineer with over 50 years of experience in instrumentation and metrology. Here is my patent list: http://www.pst.netii.net/patents.htm Among the achievements listed, I claim credit for the first disclosure of the now universal dual-d phase-frequency detector, and for the technique called Phase Margin Analysis as applied to hard disk bdrive it error analysis. The technology has evolved tremendously since the 1970's, but this was the first to show that rapid bit error analysis was possible. The internet would not be possible without this basic technique, since it would not be possible to manufacture hard disks fast enough. Another significant invention is Binary Sampling. I will talk more about this later, but some information is on my web site at http://www.pst.netii.net/sampler/index.htm also starting on page 6 of http://www.pst.netii.net/pdfs/tdrpaper.pdf One of the significant advantages of the Binary Sampler is the elimination of Gaussian and Impulse noise. Unlike conventional diode bridge samplers, the performance improves as the frequency increases. After working with the Binary Sampler, I am always dismayed to view the noisy graphs presented in time-nuts and other forums. The noise is hiding the interesting stuff and making it virtually impossible to understand what is actually going on. I Think the Binary Sampler can do a lot to help unravel the issues. I now intersperse replies: Hi( While you see a lot of pretty plots in GPS spec sheets showing clean looking sawtooth sort of offsets marching down the page, that?s not what I see on a real receiver. The real data, even compared to a 5071A is much more random. It will indeed ?hang?, but it also will reverse far more often than the pretty data sheets suggest. A simple model would be to add the sawtooth to some sort of random process. The sawtooth comes from the TCXO, the random looking stuff comes from the GPS solution. The oscillator in most timing modules is one form or another of a TCXO. Often they have digital compensation (one way or another). Their frequency versus temperature curves are not the simple third order curve you would expect from a bare crystal. They have a much higher order frequency versus temperature curve (6th, 8th ?). That makes even the simple ?frequency goes down when temp goes up? decision pretty tough. If they are doing some sort of auto correction TCXO based on the GPS it would get even more crazy. In that case the curve would be changing real time. Since the sawtooth changes multiple ?runs? per minute in a room that holds 2C / 30 minutes, you could guess that a control of 0.01C would be needed to have any luck steering the oscillator. It?s nowhere near that simple, so that?s not even up to the ?wild guess? level of confidence. If it?s close, that?s not going to be very easy all by it?s self. A double loop control is likely to be needed. Combine the random jitter with the (possibly) tough temperature control problem, and frequency reversals - this is a real can of worms. ??? Way lots easier approach: 1) You already need a CPU to set up the GPS, read the sawtooth data stream and do a control loop. It?s free / same with either approach. 2) Rip a VCTCXO out of something (or buy one cheap). 3) PWM control the TCXO, use it as your CPU clock 4) Generate a PPS with a timer output on the CPU. 5) Do a cheap / simple / easy TDC on the GPS pps, it will cost less that what ever was going to drive the heater. Now you have a GPSDO with a much lower jitter PPS output. You need to write from scratch code for the CPU either way. The code for the GPSDO is probably simpler than the temperature control code. It?s certainly no more difficult. This way you have an output at what ever the TCXO frequency is for ?other stuff?. Bob Thanks, Bob. I don't propose using temperature to control the GPS clock. I plan to use a AD9912 DDS (1GHz 48Bit 4uHz 0.19ps $59@Newark.) On Mar 5, 2014, at 6:48 PM,
Re: [time-nuts] Another atomic clock question
To the Mike that posted: http://www.pst.netii.net/patents.htm - I tried going to your site - can't reach it. Is the site operational? I wanted to take a look at your patents. Thanks, John Westmoreland == Jon, It's working OK from Edinburgh at 07:08 UTC. David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
