[time-nuts] Correcting jitter on the 1PPSsignalfromaGPSreceiver.

Peter Reilley peter at reilley.com
Sun Sep 14 14:20:06 EDT 2014

I am beginning to understand the complexity of these issues
thanks to everyone's help. 


-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Tom Van
Sent: Sunday, September 14, 2014 2:06 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Correcting jitter on the

> 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.


time-nuts mailing list -- time-nuts at febo.com To unsubscribe, go to
and follow the instructions there.

More information about the time-nuts mailing list