Hi Actually your “best case” is where the clock in the Res-T is *not* 12.50400000000000 MHz or a frequency that is +/- (N * 40 ppb) of that frequency. If it is, you get a “hanging bridge” in the data. At +/- (N * 20 ppb) you don’t get the classic hanging bridge, but you still get a bias. All of that assumes for simplicity that the sawtooth is at 40 ns rather than just a bit off from there.
Bob On Sep 14, 2014, at 2:06 PM, Tom Van Baak <[email protected]> wrote: >> They say that the system clock is 12.504 MHz and that they use both the >> rising and falling edges. That is about 40 nS between quantization time >> slots. The PPS can only appear on a 40 nS edge. I should be seeing >> 40 nS jumps in the waveforms. I do see ~40 nS jumps but they are less >> common. > > "The PPS can only appear on a 40 ns edge" -- of the imprecise, unstable, > uncompensated, unshielded, crystal oscillator on the Resolution-T board. It > may be 12.504 MHz, but it certainly isn't (and not intended to be) > 12.504000000 MHz. There's also instability in your 'scope or counter. Thus > you will see significant jitter, drift, and wander in the observed 40 ns > edges. All this is normal and expected any time you "beat" two oscillators > against each other. > > The net result is that the jumps are very evenly (and not Gaussian) > distributed anywhere from 0 ns to 40 ns. Again, look at the raw data, plots, > and histograms that I provided. Especially the "zebra" plots which show just > how varied the sawtooth error is over the span of minutes, hours, and days: > > http://leapsecond.com/pages/MG1613S/tic-72-hour.gif (3600x1800 pixels!) > >> The waveform timing is clearly quantized but I am seeing ~2 nS jumps. >> My scope is a Rigol DS2202 which samples at 1 GSP in 2 channel mode. >> Could this 2 nS quantization be a result of the scope? Perhaps I should >> get my 400 MHz analog scope out (Tek 2465B) and repeat the measurements? > > Off-list you mentioned you don't have a ns or sub-ns time interval counter, > so yes, I guess you should try the analog 'scope. I'm wondering now if your > GPS receiver more stable than your scope's timebase. > > /tvb > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
