Re: [time-nuts] Question about effect of sample interval on ADEV
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Re: [time-nuts] Question about effect of sample interval on ADEV
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Re: [time-nuts] Question about effect of sample interval on ADEV
Hi Hans, If you're familiar with the windows or unix command line then the tools and methods I use may be useful. Otherwise perhaps it's best to use standard GUI packages, like HyperTerminal, CoolTerm, Plotter, Stable32, TimeLab, etc. Note that TimeLab includes data capture capabilities for all the common instruments that we use so you don't need the CoolTerm step at all. That is, Timelab will directly capture data from a hp 53132 either over serial or GPIB/Prologix. So I highly recommend this approach for newbies and oldtimers alike. The 0.1 second jitter seems high. Yes, perhaps that is a problem with CoolTerm itself. Again, if you use TimeLab to acquire your data you can avoid using CoolTerm completely. If you are a programmer or windows command line person, the tool I use to collect, timestamp, and log all my raw data is comlog. It's under my www.leapsecond.com/tools/ directory. /tvb - Original Message - From: Hans Holzach h.holz...@vtxmail.ch To: time-nuts@febo.com Sent: Monday, July 08, 2013 10:03 PM Subject: Re: [time-nuts] Question about effect of sample interval on ADEV FYI: I tend to record all serial (RS232/GPIB/USB/LAN) data from counters, analyzers, receivers, environmental sensors with a precision MJD prefix. This allows both tight correlation among different instruments in the lab and also allows ADEV-like tools to estimate, and then gradually refine to high levels of precision, the actual data rate, during data collection. Yes, it adds a few extra bytes, but it can be valuable information sometimes and storage is cheaper than it was a decade ago. /tvb tom, as a newbie i'd be happy about a few hints how you do this. i use a prologix controller to read data lines from a 53132a counter. the data is then recorded by a terminal application (CoolTerm). the terminal application can add a timestamp to each line. however, even when in time arming or external arming (1pps from gpsdo) mode, the time stamp intervals vary significantly by up to maybe 0.1s, probably because the stamp is given by the terminal application and not by the counter. furthermore, ulrich's plotter program can't read CoolTerm's timestamp format, so i have to manipulate it in excel first before ulrich's plotter can process it... thank you, hans ___ 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] Question about effect of sample interval on ADEV
John, After a night's sleep and a rereading of your post I finally realized what I was doing wrong. I did not understand the the role of the sampling interval setting and the display rate setting on the 5370. When I follow the process below the results are totally consistent. Sorry to taken your time and thanks all for your help. Now to find the original issue. Bob Darby On 7/7/2013 8:57 PM, John Miles wrote: So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
Bob, Sorry, I'm not sure, if I've understood the issue - what exactly did you wrong? Thank you Volker Am 08.07.2013 14:48, schrieb Robert Darby: John, After a night's sleep and a rereading of your post I finally realized what I was doing wrong. I did not understand the the role of the sampling interval setting and the display rate setting on the 5370. When I follow the process below the results are totally consistent. Sorry to taken your time and thanks all for your help. Now to find the original issue. Bob Darby On 7/7/2013 8:57 PM, John Miles wrote: So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
Volker, Silly mistake, I was changing the sample interval in the acquire menu of TimeLab and it did not match the 5370B. When I changed the display rate control and used the monitor command to set the sampling interval as directed by John all was right with the world. Tom, What did you do to solve the battery charging circuit issues in the FTS 1050A? Thanks, Bob Darby On 7/8/2013 2:26 PM, Volker Esper wrote: Bob, Sorry, I'm not sure, if I've understood the issue - what exactly did you wrong? Thank you Volker Am 08.07.2013 14:48, schrieb Robert Darby: John, After a night's sleep and a rereading of your post I finally realized what I was doing wrong. I did not understand the the role of the sampling interval setting and the display rate setting on the 5370. When I follow the process below the results are totally consistent. Sorry to taken your time and thanks all for your help. Now to find the original issue. Bob Darby On 7/7/2013 8:57 PM, John Miles wrote: So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
No prob! It's a complicated business. -- john, KE5FX Miles Design LLC -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Robert Darby Sent: Monday, July 08, 2013 5:48 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Question about effect of sample interval on ADEV John, After a night's sleep and a rereading of your post I finally realized what I was doing wrong. I did not understand the the role of the sampling interval setting and the display rate setting on the 5370. When I follow the process below the results are totally consistent. Sorry to taken your time and thanks all for your help. Now to find the original issue. Bob Darby On 7/7/2013 8:57 PM, John Miles wrote: So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
FYI: I tend to record all serial (RS232/GPIB/USB/LAN) data from counters, analyzers, receivers, environmental sensors with a precision MJD prefix. This allows both tight correlation among different instruments in the lab and also allows ADEV-like tools to estimate, and then gradually refine to high levels of precision, the actual data rate, during data collection. Yes, it adds a few extra bytes, but it can be valuable information sometimes and storage is cheaper than it was a decade ago. /tvb - Original Message - From: John Miles j...@miles.io To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Monday, July 08, 2013 2:17 PM Subject: Re: [time-nuts] Question about effect of sample interval on ADEV No prob! It's a complicated business. -- john, KE5FX Miles Design LLC -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Robert Darby Sent: Monday, July 08, 2013 5:48 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Question about effect of sample interval on ADEV John, After a night's sleep and a rereading of your post I finally realized what I was doing wrong. I did not understand the the role of the sampling interval setting and the display rate setting on the 5370. When I follow the process below the results are totally consistent. Sorry to taken your time and thanks all for your help. Now to find the original issue. Bob Darby On 7/7/2013 8:57 PM, John Miles wrote: So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
FYI: I tend to record all serial (RS232/GPIB/USB/LAN) data from counters, analyzers, receivers, environmental sensors with a precision MJD prefix. This allows both tight correlation among different instruments in the lab and also allows ADEV-like tools to estimate, and then gradually refine to high levels of precision, the actual data rate, during data collection. Yes, it adds a few extra bytes, but it can be valuable information sometimes and storage is cheaper than it was a decade ago. /tvb tom, as a newbie i'd be happy about a few hints how you do this. i use a prologix controller to read data lines from a 53132a counter. the data is then recorded by a terminal application (CoolTerm). the terminal application can add a timestamp to each line. however, even when in time arming or external arming (1pps from gpsdo) mode, the time stamp intervals vary significantly by up to maybe 0.1s, probably because the stamp is given by the terminal application and not by the counter. furthermore, ulrich's plotter program can't read CoolTerm's timestamp format, so i have to manipulate it in excel first before ulrich's plotter can process it... thank you, hans ___ 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] Question about effect of sample interval on ADEV
This is a question that has probably been addressed on the list and in various texts but I've been unable to find an answer that I can fathom so here's a request for some info about the behavior of TimeLab (and probably all other similar programs). I have been trying to find the source of some periodic noise that appears when using a 5370B to measure an FTS 1050B against a 5065B. The noise manifests itself varying from 12s to 20s in a repetitive fashion. I asked C. Dawson about this and one of his suggestions was to try a longer sampling period. Down the rabbit hole I went! I ran four trials in succession at sample intervals of .07s, .25s, .5s, and 1s. The result is as if the adev ,modified, and Hadamard curves have been slid down and to the right along the noise floor of the 5370. My assumption, apparently incorrect, was that the software would take the sampling interval into account so that I would get essentially the same plot. When I edit a plot changing the sample interval, the trace remains essentially unchanged and this seems inconsistent with the results noted above. Can anyone explain in relatively simple terms what I'm missing? Thanks, Bob Darby ___ 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] Question about effect of sample interval on ADEV
Hi Bob, Send me the raw data and I'll have a look to confirm or explain your results. I've seen this in some of my FTS 1050 also; it's always been the fault of the battery charger circuit. /tvb - Original Message - From: Robert Darby bobda...@triad.rr.com To: time-nuts@febo.com Sent: Sunday, July 07, 2013 12:27 PM Subject: [time-nuts] Question about effect of sample interval on ADEV This is a question that has probably been addressed on the list and in various texts but I've been unable to find an answer that I can fathom so here's a request for some info about the behavior of TimeLab (and probably all other similar programs). I have been trying to find the source of some periodic noise that appears when using a 5370B to measure an FTS 1050B against a 5065B. The noise manifests itself varying from 12s to 20s in a repetitive fashion. I asked C. Dawson about this and one of his suggestions was to try a longer sampling period. Down the rabbit hole I went! I ran four trials in succession at sample intervals of .07s, .25s, .5s, and 1s. The result is as if the adev ,modified, and Hadamard curves have been slid down and to the right along the noise floor of the 5370. My assumption, apparently incorrect, was that the software would take the sampling interval into account so that I would get essentially the same plot. When I edit a plot changing the sample interval, the trace remains essentially unchanged and this seems inconsistent with the results noted above. Can anyone explain in relatively simple terms what I'm missing? Thanks, Bob Darby ___ 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] Question about effect of sample interval on ADEV
Bob, On 07/07/2013 09:27 PM, Robert Darby wrote: This is a question that has probably been addressed on the list and in various texts but I've been unable to find an answer that I can fathom so here's a request for some info about the behavior of TimeLab (and probably all other similar programs). I have been trying to find the source of some periodic noise that appears when using a 5370B to measure an FTS 1050B against a 5065B. The noise manifests itself varying from 12s to 20s in a repetitive fashion. I asked C. Dawson about this and one of his suggestions was to try a longer sampling period. Down the rabbit hole I went! I ran four trials in succession at sample intervals of .07s, .25s, .5s, and 1s. The result is as if the adev ,modified, and Hadamard curves have been slid down and to the right along the noise floor of the 5370. My assumption, apparently incorrect, was that the software would take the sampling interval into account so that I would get essentially the same plot. When I edit a plot changing the sample interval, the trace remains essentially unchanged and this seems inconsistent with the results noted above. Can anyone explain in relatively simple terms what I'm missing? TimeLab will use the sampling interval you gave it or it learned during monitoring and scale results accordingly if properly given. If you have systematic noise, try loading it into a FFT rather than doing an ADEV. The trouble is that a sine modulation will show up as multiple bumps on the ADEV but a single spike on FFT. If you have multiple signals, it becomes easier to identify in the FFT. 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] Question about effect of sample interval on ADEV
This won't be a sampling-interval issue. It sounds like a beat note. To diagnose it, you can use the 5370B in frequency mode (with its internal timebase) to measure the frequency of the 5065B and the FTS 1050B. Subtract the two readings, then see if the reciprocal of the frequency difference corresponds to the location and spacing of the periodic ADEV bumps. If so, that's likely to be the explanation, and you can confirm it by tweaking the FTS 1050B's frequency and seeing if the beatnote moves accordingly. As far as getting rid of the artifact is concerned, it may help to use double-shielded cables, although I don't know if the isolation between the START and STOP inputs on the 5370B is good enough to eliminate the possibility of beatnotes in a TI measurement with HF signals on both jacks. If you are feeding the 5/10 MHz inputs to both START and STOP inputs, try using a 1-pps divider on the START source. You could also try using the 5370B in frequency-count mode, with the 5065A as an external reference and the FTS 1050B at the STOP input. There will be a reduction in ADEV fidelity due to the dead time but it will probably be less objectionable than the beatnote ripple. -- john, KE5FX Miles Design LLC My assumption, apparently incorrect, was that the software would take the sampling interval into account so that I would get essentially the same plot. When I edit a plot changing the sample interval, the trace remains essentially unchanged and this seems inconsistent with the results noted above. Can anyone explain in relatively simple terms what I'm missing? Thanks, Bob Darby ___ 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] Question about effect of sample interval on ADEV
On 07/07/2013 11:38 PM, John Miles wrote: This won't be a sampling-interval issue. It sounds like a beat note. To diagnose it, you can use the 5370B in frequency mode (with its internal timebase) to measure the frequency of the 5065B and the FTS 1050B. Subtract the two readings, then see if the reciprocal of the frequency difference corresponds to the location and spacing of the periodic ADEV bumps. If so, that's likely to be the explanation, and you can confirm it by tweaking the FTS 1050B's frequency and seeing if the beatnote moves accordingly. As far as getting rid of the artifact is concerned, it may help to use double-shielded cables, although I don't know if the isolation between the START and STOP inputs on the 5370B is good enough to eliminate the possibility of beatnotes in a TI measurement with HF signals on both jacks. If you are feeding the 5/10 MHz inputs to both START and STOP inputs, try using a 1-pps divider on the START source. You could also try using the 5370B in frequency-count mode, with the 5065A as an external reference and the FTS 1050B at the STOP input. There will be a reduction in ADEV fidelity due to the dead time but it will probably be less objectionable than the beatnote ripple. I had a measurement with a sine being overlaid, and just for fun I wrote a small pre-processing program that put a pair of zeros close to the unity circle and about the right frequency. The end result was very clean and the unwanted artifact was removed. Care in ensuring unity gain was needed, but once that was done it worked like a charm. This trick is a bit dirty, but keeping the Q high on the zeros makes sure that the other noise is not affected gravely, and the ripples of the sine was cleaned out. The benefit of doing an equalizer to notch it out compared to trying to measure the amplitude and phase of a sine and then subtract the estimated sine is what the notching method will be relatively insensitive to amplitude, phase and frequency errors that will limit the usefulness of the perfect matching. Any slow shifts will also be fairly ignored. I used a very rough period estimation to tune it. 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] Question about effect of sample interval on ADEV
Thanks to all who responded. I didn't phrase my question very well I'm afraid. The periodic noise/beat note issue is what lead me to try a different sample interval. Previously I had always let TimeLab set the sample interval (about .07s for the5370B). I was surprised by the difference in the adev traces when I varied the sample interval from .07s to .25s to .5s to 1.0s and that is what I hoped someone could explain. When I edit a trace and change the sample interval there is not a substantial change to the Tau / Sigma (Tau) values yet when I actually run at the different sample intervals I get minimum values for each run of 400s 5.60e-13, 600s 1.70e-13, 1000s 9.55e-14, 3000s 4.15e-14. The traces are totally different; same oscillators and counter, just different sample intervals. That's what I hoping one of you could explain. John, I'll explore the the beat note issue to see if that's the problem. Tom, since I get a similar issue when I swap the FTS for an Austron (more battery chargers) I don't think the FTS is the culprit. Thanks again. Bob On 7/7/2013 5:38 PM, John Miles wrote: This won't be a sampling-interval issue. It sounds like a beat note. To diagnose it, you can use the 5370B in frequency mode (with its internal timebase) to measure the frequency of the 5065B and the FTS 1050B. Subtract the two readings, then see if the reciprocal of the frequency difference corresponds to the location and spacing of the periodic ADEV bumps. If so, that's likely to be the explanation, and you can confirm it by tweaking the FTS 1050B's frequency and seeing if the beatnote moves accordingly. As far as getting rid of the artifact is concerned, it may help to use double-shielded cables, although I don't know if the isolation between the START and STOP inputs on the 5370B is good enough to eliminate the possibility of beatnotes in a TI measurement with HF signals on both jacks. If you are feeding the 5/10 MHz inputs to both START and STOP inputs, try using a 1-pps divider on the START source. You could also try using the 5370B in frequency-count mode, with the 5065A as an external reference and the FTS 1050B at the STOP input. There will be a reduction in ADEV fidelity due to the dead time but it will probably be less objectionable than the beatnote ripple. -- john, KE5FX Miles Design LLC My assumption, apparently incorrect, was that the software would take the sampling interval into account so that I would get essentially the same plot. When I edit a plot changing the sample interval, the trace remains essentially unchanged and this seems inconsistent with the results noted above. Can anyone explain in relatively simple terms what I'm missing? Thanks, Bob Darby ___ 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] Question about effect of sample interval on ADEV
-Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Robert Darby Sent: Sunday, July 07, 2013 3:33 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Question about effect of sample interval on ADEV Thanks to all who responded. I didn't phrase my question very well I'm afraid. The periodic noise/beat note issue is what lead me to try a different sample interval. Previously I had always let TimeLab set the sample interval (about .07s for the5370B). I was surprised by the difference in the adev traces when I varied the sample interval from .07s to .25s to .5s to 1.0s and that is what I hoped someone could explain. When I edit a trace and change the sample interval there is not a substantial change to the Tau / Sigma (Tau) values yet when I actually run at the different sample intervals I get minimum values for each run of 400s 5.60e-13, 600s 1.70e-13, 1000s 9.55e-14, 3000s 4.15e-14. The traces are totally different; same oscillators and counter, just different sample intervals. That's what I hoping one of you could explain. So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
John, In the past I've allowed TimeLab to pick the sampling interval (usually .07s for the 5370B) but when I use Acquire, Sampling Interval and set that to 1 sec I get very different results. Apparently the result is not the same as Edit, Trace, Sample Interval. All of the foregoing in TI mode. BTW, thanks for the program. Bob Darby On 7/7/2013 8:57 PM, John Miles wrote: -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Robert Darby Sent: Sunday, July 07, 2013 3:33 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Question about effect of sample interval on ADEV Thanks to all who responded. I didn't phrase my question very well I'm afraid. The periodic noise/beat note issue is what lead me to try a different sample interval. Previously I had always let TimeLab set the sample interval (about .07s for the5370B). I was surprised by the difference in the adev traces when I varied the sample interval from .07s to .25s to .5s to 1.0s and that is what I hoped someone could explain. When I edit a trace and change the sample interval there is not a substantial change to the Tau / Sigma (Tau) values yet when I actually run at the different sample intervals I get minimum values for each run of 400s 5.60e-13, 600s 1.70e-13, 1000s 9.55e-14, 3000s 4.15e-14. The traces are totally different; same oscillators and counter, just different sample intervals. That's what I hoping one of you could explain. So the only difference between the test setups is the setting of the Display Rate control on the 5370, correct? You're allowing TimeLab to estimate the sample rate automatically, and giving it enough time to converge on a stable reading before hitting 'Start Measurement'? You're correct in that changing the real-world sample rate should yield results that are identical (or at least very similar) to resampling the phase data after the fact. In frequency mode, dead time between readings would make that an iffy proposition, but for data taken in TI mode the outcomes should be close. -- john, KE5FX Miles Design LLC ___ 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] Question about effect of sample interval on ADEV
Hi, to echo the comments John and Magnus made, I've encountered similar issues in the past when using my HP5370B's to compare my FTS 1050 to other standards. The fix involved using double shielded RG 400 style cables in my lab (I realize the RG 400 standard is not really a standard any more..) I had previously terminated all of the relevant unused inputs and outputs of my time nuts gear with 50 ohm terminators. I've also encountered similar issues with several standalone Datum 1000B's and needed to add ferrite chokes to the power and double shielded signal cables connected to the Datum 1000B to solve the issues. I suspect the Datums would work better inside of a shielded enclosure with bypassed power leads vs sitting on a bench in my lab. My recollection is that the internal oscilator inside of the FTS 1050 is typically similar to the Datum 1000B. My BVA 8600 seems relatively immune to these issues. As a side note I've also found I get better results when using 3 to 6 dB of attenuation between the output of my particular FTS1050 and the inputs of my particular HP5370B's (I seem to recall there are some other threads in the archives about the need to optimize the signal levels to get the best results from the HP5370 series counters.) Your results may differ. Best regards Mark S Message: 5 Date: Sun, 7 Jul 2013 14:38:09 -0700 From: John Miles j...@miles.io To: 'Tom Van Baak' t...@leapsecond.com, 'Discussion of precise time and frequency measurement' time-nuts@febo.com Subject: Re: [time-nuts] Question about effect of sample interval on ADEV Message-ID: 0b8501ce7b5a$47ea8cf0$d7bfa6d0$@miles.io Content-Type: text/plain; charset=us-ascii This won't be a sampling-interval issue. It sounds like a beat note. To diagnose it, you can use the 5370B in frequency mode (with its internal timebase) to measure the frequency of the 5065B and the FTS 1050B. Subtract the two readings, then see if the reciprocal of the frequency difference corresponds to the location and spacing of the periodic ADEV bumps. If so, that's likely to be the explanation, and you can confirm it by tweaking the FTS 1050B's frequency and seeing if the beatnote moves accordingly. As far as getting rid of the artifact is concerned, it may help to use double-shielded cables, although I don't know if the isolation between the START and STOP inputs on the 5370B is good enough to eliminate the possibility of beatnotes in a TI measurement with HF signals on both jacks. If you are feeding the 5/10 MHz inputs to both START and STOP inputs, try using a 1-pps divider on the START source. You could also try using the 5370B in frequency-count mode, with the 5065A as an external reference and the FTS 1050B at the STOP input. There will be a reduction in ADEV fidelity due to the dead time but it will probably be less objectionable than the beatnote ripple. -- john, KE5FX Miles Design LLC My assumption, apparently incorrect, was that the software would take the sampling interval into account so that I would get essentially the same plot. When I edit a plot changing the sample interval, the trace remains essentially unchanged and this seems inconsistent with the results noted above. Can anyone explain in relatively simple terms what I'm missing? Thanks, Bob Darby ___ 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.
