[time-nuts] Correcting jitter on the 1 PPS signalfromaGPSreceiver.

Peter Reilley peter at reilley.com
Sun Sep 14 12:38:30 EDT 2014


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-bounces at 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 <peter at 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-bounces at 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 at 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 at 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 at febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.



More information about the time-nuts mailing list