[time-nuts] How do I measure oscillator frequency using 1pps?

David Kirkby david.kirkby at onetel.net
Sat Jul 9 16:55:38 EDT 2005

I've now got

1) Stanford PRS10 rubidium standard
2) Motorola M12+ timing GPS receiver with a 1 pps output.
3) HP 5370B time interval counter.

I'd like to look at the drift of the rubidium before I try to steer it 
with the PLL. Can anyone explain how to do this with the 5370B?

I understand how you can measure the drift between two sources at 10MHz, 
by looking at the rate at which the time interval is changing, but I 
don't understand how to do it with the 1pps GPS signal, since the jitter 
on the 1pps will be of the same order (or larger) than the time period 
of the 10MHz source. If I start Even if you fiddle the cable lengths so 
the time interval between the 1pps and the rubidium is 50ns, the jitter 
on the GPS means a value of 1ns could be 1ns or 101ns, and you would 
have no idea at all.

Perhaps the way to do it is to use the rubidium as a start, and the 1pps 
as a stop. Then the TI will be somewhere in the range 0 to 1 second, and 
the jitter can be averaged out in software.

I'm basically confused, as I am sure you can tell.

David Kirkby,

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/

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