[ntp:questions] How exact are the PPS pulses of common GPSses?

Ralph Aichinger ralph at pangea.at
Wed Feb 13 13:29:13 UTC 2013

Terje Mathisen <"terje.mathisen at tmsw.no"> wrote:
> Unless you replace the motherboard clock source, anything below ~us 
> precision is wasted.

Good to know. So basically the 1 or 2µs jitter I get after everything
has had time to settle down is the maximum archievable unless you
use rather exotic hardware.

> I have seen reports that the original Motorola Oncore UT+ had something 
> like 30 ns RMS jitter (after applying the sw saw-tooth correction), 
> while the $35 Sure board has been tested by one of the time-nuts people 
> at ~25 ns?

That is great, so basically jitter is a non-issue compared to standard
computer hardware, and I am pleasantly surprised that the Sure board
is that good. 

Has anybody checked the PPS output for constant shift against
UTC? Is it possible that the pulses are off with a constant offset,
even if they have very little jitter? Or is this unlikely from what
happens inside the receiver?

/ralph -- I am waiting for the first tutorial how to build a 
          rubidium-disciplined Raspberry Pi ;)

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