Re: [time-nuts] Correcting jitter on the 1 PPS signal fromaGPSreceiver.
Ok, did the math, a 4ns risetime should be ok on a 200MHz scope. You likely won't see the oscillations and reflections visible in Toms 58503A plots for example, they are faster than the risetime. Bye, Said Sent From iPhone > On Sep 14, 2014, at 8:35, Said Jackson via time-nuts > wrote: > > Peter, > > You don't need nor do you want a 50 ohms end-termination on a > series-terminated 50 ohms coax cable. > > This has been discussed here extensively before, please check the archives. > Your last sentence is not correct. > > Also, you are running into your scope's BW limit if you are measuring a 4ns > risetime with a 200MHz scope.. > > Bye, > Said > > Sent From iPhone > >> On Sep 14, 2014, at 6:19, "Peter Reilley" 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.
Re: [time-nuts] Correcting jitter on the 1 PPS signal fromaGPSreceiver.
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 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.
Re: [time-nuts] Correcting jitter on the 1 PPS signal fromaGPSreceiver.
Peter, You don't need nor do you want a 50 ohms end-termination on a series-terminated 50 ohms coax cable. This has been discussed here extensively before, please check the archives. Your last sentence is not correct. Also, you are running into your scope's BW limit if you are measuring a 4ns risetime with a 200MHz scope.. Bye, Said Sent From iPhone > On Sep 14, 2014, at 6:19, "Peter Reilley" 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.
Re: [time-nuts] Correcting jitter on the 1 PPS signal fromaGPSreceiver.
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.
Re: [time-nuts] Correcting jitter on the 1 PPS signal fromaGPSreceiver.
Pete, I have not measured the Resolution-T clock frequency. Be aware that the 1PPS timing spec in the data sheet (e.g., N ns from UTC) is not related to the CPU clock frequency. The CPU clock is directly related to the range of the sawtooth corrections, by the very definition of "quantization". Some receivers use both edges of the clock so you have to be careful about guessing clock rate from sawtooth range alone. To give you a feel for Resolution-T sawtooth correction here's a histogram: http://leapsecond.com/pages/res-t/res-t-saw.gif 25,000 sample raw data for the plot: http://leapsecond.com/pages/res-t/res-t-saw.txt The standard deviation is 11.7 ns. Depending on how you measure, the range is 36 or 44 ns. Note the mean is about 2 ns (not 0). I'm curious if your Res-T looks the same as mine. More sawtooth examples: http://leapsecond.com/pages/MG1613S/ http://leapsecond.com/pages/vp/sawtooth.htm http://leapsecond.com/pages/m12/sawtooth.htm /tvb - Original Message - From: "Peter Reilley" To: "'Discussion of precise time and frequency measurement'" Sent: Saturday, September 13, 2014 5:52 PM Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal fromaGPSreceiver. >I don't see any mention of sawtooth correction in their documentation. > I take that to imply that sawtooth correction is not necessary to get > the 15 nS that is spec'ed? > > Does the 15 nS imply that the internal clock is 33 MHz? That is: +-15 nS > is 30 nS which is 33 MHz. Is that correct? Or do they need a higher > internal > clock so that all errors sum to less than 15 nS? > > Pete. ___ 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.
