Re: [time-nuts] Tbolt Damping setting
Good points, and You got 4 1/2 out of five correct, Not bad at all. Ha ha - thank you teacher! Fairy nuff, yes, your plots show the long-term effects. I would like to know what the best time-constant is to use. I appreciate that everyone's will be different, depending on individual characteristics of the Thunderbolts, and also (perhaps more importantly) the aerial and its position. However, I think it would be interesting to at least see the relative differences for one location. I recently learnt that our national mapping organisation (The Ordnance Survey) average the results from their L1/L2 Leica 1200 system receivers, for two hours. Is the oscillator in the Leica significantly worse than that in out Thunderbolts, or could we also benefit from a time-constant of longer than 1000 seconds? I will try to find a quiet rubidium, and do some comparisons against that - the results should, at least, be valid out to a few thousand seconds. I also plan to try reducing the signal level threshold (from the current 4AMU) as recently suggested, and try to see some quantifiable results. TTFN, Peter Vince (G8ZZR, London, England) ___ 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] Tbolt Damping setting
Peter PV) However, I think it would be interesting to at least see the relative differences for one location. The relative difference can be seen in the Green Dac plot, which shows the total PP noise at 50 Sec and slower. The Dac is scaled to 1e-11 per division, for RMS or ADEV, divide PP by about 5. As you pointed out the Tbolt and LH can NOT do 1 sec noise directly without an external reference, BUT by looking at the excess nose that is applied to the DAC, you can see what is happening at one sec, or 10 or 100. Ideally The Dac should not be forced to move at a freq below the TC setting, If it does that is added noise. By the way, To force a similar sort of 50 ns sawtooth phase error waveform when using an external reference, Use the Osc phase setting to invert the phase of the Tbolt OSC sync timing. PV) Is the oscillator in the Leica significantly worse than that in out Thunderbolts, or could we also benefit from a time-constant of longer than 1000 seconds? I know little about anything except Tbolts but If you show me a couple of good plots, with and without GPS control, I could probable answer that. PV) I will try to find a quiet rubidium Depending on what errors you are most concerned with, Phase short term or long term , Low tau ADV or High Tau ADV, (or hold over, yek) May not even be necessary for it to be a low noise quiet one Have fun ws (in central California) ***- Original Message - From: Peter Vince pvi...@theiet.org To: WarrenS warrensjmail-...@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, December 16, 2009 4:54 AM Subject: Re: [time-nuts] Tbolt Damping setting Good points, and You got 4 1/2 out of five correct, Not bad at all. Ha ha - thank you teacher! Fairy nuff, yes, your plots show the long-term effects. I would like to know what the best time-constant is to use. I appreciate that everyone's will be different, depending on individual characteristics of the Thunderbolts, and also (perhaps more importantly) the aerial and its position. However, I think it would be interesting to at least see the relative differences for one location. I recently learnt that our national mapping organisation (The Ordnance Survey) average the results from their L1/L2 Leica 1200 system receivers, for two hours. Is the oscillator in the Leica significantly worse than that in out Thunderbolts, or could we also benefit from a time-constant of longer than 1000 seconds? I will try to find a quiet rubidium, and do some comparisons against that - the results should, at least, be valid out to a few thousand seconds. I also plan to try reducing the signal level threshold (from the current 4AMU) as recently suggested, and try to see some quantifiable results. TTFN, Peter Vince (G8ZZR, London, England) ___ 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] Tbolt Damping setting
Thank you for your explanation. Your Lady Heather plot prompts a couple of questions though: 1) Presumably you created the 40ns phase step by changing the output timing offset? 2) Presumably, again, the plotted data is from the self reported data from the Thunderbolt? I have been running a series of tests myself this year, but on looking at the results, it became clear - and I should have twigged this earlier - that all the Thunderbolt can do is report the differences between itself and the noisy GPS signal. Whereas what I really wanted was a comparison to a stable external standard. Sadly I don't have TVB's Maser or 5071s, but I suspect that such a comparison would give a rather different plot. Tom has talked about these factors on his page at http://www.LeapSecond.com/pages/tbolt-tc/ just showing MDEV plots. Tom: would you have the time to replicate Warren's experiment, but show the phase and frequency plots with respect to your Maser or 5071? As an aside, at the beginning of the year when the TAPR offer was on, it was suggested on here that the time constant be set to that where the ADEV plot reaches a minimum whilst on holdover. A couple of days after turning on, mine was about 700 seconds. Now, nine months continuous operation later, and with the Thunderbolt in the recommended cardboard box to protect from drafts, the plot now reaches a minimum at about 2500 seconds! Peter ___ 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] Tbolt Damping setting
Peter and all, Good points, and You got 4 1/2 out of five correct, Not bad at all. #1) YES, The easy way I used to make the controlled phase error steps was by entering a new number into the cable delay, which is limited to under 50ns change. #2) Yes, this is the self reported Tbolt data plotted by LH. #3) Yes, All the Thunderbolt can do is report the differences between itself and the (short term) noisy GPS signal. #4) Yes, what is really desired is a comparison to a stable external standard. #5) Yes, YesNO, No, ... Such a comparison would give a rather different plot. 5a) Very much Yes, when plotting unfiltered display data, (The New LH can filter the plots, should use 100 + sec to minimize the GPS noise) 5b) somewhat Yes looking at times under 500 sec or so. and the important thing, and the only thing I was trying to show is: 5c) NO for data longer than 1000 sec, where the GPS is going to be pretty much the most accurate thing that most have. So with the plots I made, showing the Basic long term TC time and shape, they are as close as anything you are going to get using an external ref. On the other hand, The high freq wiggles in the 0 to 500 sec range, are not real. They are the noisy GPS and not the OSC. If you want to run the same test at faster TC or with more accuracy, JUST need to increase the Phase error by about times ten, so that the GPS nose is NOT a limiting factor. Will give the same basic shape, just less GPS noise wiggles. The basic shape of what I'm showing on the plots is valid, More so in fact than you would get with most external References. Concerning Toms ADEV numbers. Two different uses, His Plots show what the noise across the whole time span is, at the time the data was taken, These plots show Why, and by changing the filter setting show the relative noise at different time spans with different setting, with Post processing. ws *** Thank you for your explanation. Your Lady Heather plot prompts a couple of questions though: 1) Presumably you created the 40ns phase step by changing the output timing offset? 2) Presumably, again, the plotted data is from the self reported data from the Thunderbolt? I have been running a series of tests myself this year, but on looking at the results, it became clear - and I should have twigged this earlier - that all the Thunderbolt can do is report the differences between itself and the noisy GPS signal. Whereas what I really wanted was a comparison to a stable external standard. Sadly I don't have TVB's Maser or 5071s, but I suspect that such a comparison would give a rather different plot. Tom has talked about these factors on his page at http://www.LeapSecond.com/pages/tbolt-tc/ just showing MDEV plots. Tom: would you have the time to replicate Warren's experiment, but show the phase and frequency plots with respect to your Maser or 5071? As an aside, at the beginning of the year when the TAPR offer was on, it was suggested on here that the time constant be set to that where the ADEV plot reaches a minimum whilst on holdover. A couple of days after turning on, mine was about 700 seconds. Now, nine months continuous operation later, and with the Thunderbolt in the recommended cardboard box to protect from drafts, the plot now reaches a minimum at about 2500 seconds! Peter ___ 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.
