Hi If you are seeing modulo 2 ns jumps, then there is something in your setup causing them. The Res-T can only put out something about every 40 ns.
That edge is locked to nothing at all, so it does drift. If your particular 12.504 MHz clock is off by 1 ppm, then it’s edge will drift 1 us per second. That will get quantized modulo 40 ns and you will get a new edge. If your clock is within 1 ppb it will drift 1 ns per second and you will see very little change due to drift. Unless you have an OCXO on your unit, the 1 ppm is a better guess than the 1 ppb. Bob On Sep 14, 2014, at 12:38 PM, Peter Reilley <pe...@reilley.com> wrote: > Thank you for that link. I read the section of quantization error. > I am confused with what I am seeing on my scope verses what they are saying > > 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 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? > > Pete. > > > -----Original Message----- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp > Sent: Sunday, September 14, 2014 11:30 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Correcting jitter on the 1 PPS > signalfromaGPSreceiver. > > Hi > > If you look at: > > ftp://ftp.trimble.com/pub/sct/embedded/bin/Manuals/Old%20Manuals/Resolution% > 20T%20Final%20Final.pdf > > (first hit on Google for Resolution T manual, no other reason for picking > it). > > In the index, "PPS Quantization Error" is on page 46. > > On page 46 they talk about the +/- 20 ns error from sawtooth and how to > correct it out. > > Page 47 shows the plot with the sawtooth still in the signal. Page 48 shows > the plot with it removed. > > Bob > > > > On Sep 14, 2014, at 9:19 AM, Peter Reilley <pe...@reilley.com> wrote: > >> My rise time is about 4 nS. I am measuring that with my 200 MHz >> scope. I am only using 50 Ohm termination, anything else is not >> valid when using 50 Ohm coax. >> >> Pete. >> >> >> -----Original Message----- >> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Tom >> Van Baak >> Sent: Saturday, September 13, 2014 10:34 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal >> fromaGPSreceiver. >> >>> The cables are not exactly the same lengths. Differences in length >>> will result in a fixed offset. I am not concerned about such fixed >>> errors, only jitter. >>> >>> I am comparing the rising edges which is what the spec defines as the >>> reference edge. >>> >>> Pete. >> >> Pete, >> >> Correct, the survey position is determined only by the phase center of >> the antenna, not by cable length. And cable length mismatches should >> make no difference in your jitter measurements. >> >> But one thing to check is how sharp the 1PPS rising edge is -- right >> at the input to your TI counter. I use a BNC tee with one leg open >> allowing a 'scope check (set to 1M input). If your risetime is a >> couple of ns like mine is, then all is well. Slow risetime can be a huge > source of timing jitter. >> Check both 50R and 1M at the counter input. Use DC, not AC coupling. >> Use fixed trigger, never auto-trigger. Pick a trigger level that >> matches the maximum slope. >> >> Some examples of good/bad GPS 1PPS risetimes: >> http://leapsecond.com/pages/gpsdo-rise/ >> >> /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. >> >> _______________________________________________ >> 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. _______________________________________________ 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.