Re: [time-nuts] Correcting jitter on the 1 PPS signal from aGPSreceiver.
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. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Saturday, September 13, 2014 8:03 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from aGPSreceiver. Hi I'm sure they expect you to take out the sawtooth error before you do the comparison. Are you doing that? Bob On Sep 13, 2014, at 6:41 PM, Peter Reilley pe...@reilley.com wrote: I see in the Trimble Resolution T data sheet that they say that the PPS signal is within 15 nS to GPS or UTC (1 Sigma) when using an over determined solution in stationary mode.. I take this to mean that the PPS signal should be within 15 nS and that comparing 2 units that there should be no more than 30 nS between the two edges. This is comparing the rising edges. Pete. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Saturday, September 13, 2014 6:26 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from a GPSreceiver. Hi Where are you getting the 15 ns accuracy number from? When I look at the Trimble spec's they have a number of errors described (like sawtooth) that are larger than 15 ns. Bob On Sep 13, 2014, at 10:41 AM, Peter Reilley pe...@reilley.com wrote: I have 2 Trimble Resolution T receivers and I have compared the 1 PPS signal between the 2 units. They are spec'ed at 15 nS accuracy.I am seeing about 80 nS of jitter between the two. This is with about 6 satellites in view. I was thinking about ways to improve this. Since this is a stationary installation, can you use the jitter in the reported location (latitude and longitude) to correct for the 1 PPS jitter? The location data is derived using the internal GPS disciplined oscillator so both pieces of information should show the same jitter error. If you compare the reported location with the known fixed location you should be able to use that error to correct for the 1 PPS error. Does this make sense or am I missing something? 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. ___ 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 from aGPSreceiver.
Hi If it’s the same Res-T that I’ve seen the data sheet on, yes it does have sawtooth correction data coming out of it. You do have to take out the sawtooth to get it to run as well as it can. Bob On Sep 13, 2014, at 8:52 PM, Peter Reilley pe...@reilley.com wrote: 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. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Saturday, September 13, 2014 8:03 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from aGPSreceiver. Hi I'm sure they expect you to take out the sawtooth error before you do the comparison. Are you doing that? Bob On Sep 13, 2014, at 6:41 PM, Peter Reilley pe...@reilley.com wrote: I see in the Trimble Resolution T data sheet that they say that the PPS signal is within 15 nS to GPS or UTC (1 Sigma) when using an over determined solution in stationary mode.. I take this to mean that the PPS signal should be within 15 nS and that comparing 2 units that there should be no more than 30 nS between the two edges. This is comparing the rising edges. Pete. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: Saturday, September 13, 2014 6:26 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from a GPSreceiver. Hi Where are you getting the 15 ns accuracy number from? When I look at the Trimble spec's they have a number of errors described (like sawtooth) that are larger than 15 ns. Bob On Sep 13, 2014, at 10:41 AM, Peter Reilley pe...@reilley.com wrote: I have 2 Trimble Resolution T receivers and I have compared the 1 PPS signal between the 2 units. They are spec'ed at 15 nS accuracy.I am seeing about 80 nS of jitter between the two. This is with about 6 satellites in view. I was thinking about ways to improve this. Since this is a stationary installation, can you use the jitter in the reported location (latitude and longitude) to correct for the 1 PPS jitter? The location data is derived using the internal GPS disciplined oscillator so both pieces of information should show the same jitter error. If you compare the reported location with the known fixed location you should be able to use that error to correct for the 1 PPS error. Does this make sense or am I missing something? 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. ___ 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.
Re: [time-nuts] Correcting jitter on the 1 PPS signal from aGPSreceiver.
Pete, Bob, For data on a Resolution-T that I tested see http://leapsecond.com/pages/res-t/ What I found: the raw 1PPS has a standard deviation of about 13 ns; with sawtooth correction that drops to about 6 ns. If that sounds too good to be true, I can double check the raw data, or even re-run the test. I still have the same Trimble board; maybe more than one of them. So my suggestion is to try to duplicate this level of performance first, for each of your two units separately. Only then run the test comparing them against themselves. /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.
Re: [time-nuts] Correcting jitter on the 1 PPS signal from aGPSreceiver.
Offline Tom, Have you run the same sort of test on a LEA-6T, or do you know off the top of your head what the std deviation is? I had naively expected it to be spot on, but I see jumps every now and then, and I don't know whether it's something on my end, or if that's expected. Bob From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, September 13, 2014 8:42 PM Subject: Re: [time-nuts] Correcting jitter on the 1 PPS signal from aGPSreceiver. Pete, Bob, For data on a Resolution-T that I tested see http://leapsecond.com/pages/res-t/ What I found: the raw 1PPS has a standard deviation of about 13 ns; with sawtooth correction that drops to about 6 ns. If that sounds too good to be true, I can double check the raw data, or even re-run the test. I still have the same Trimble board; maybe more than one of them. So my suggestion is to try to duplicate this level of performance first, for each of your two units separately. Only then run the test comparing them against themselves. /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 from aGPSreceiver.
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.
