[time-nuts] How do I measure oscillator frequency using 1pps?
javier at nebulosa.org
Sat Jul 9 17:16:57 EDT 2005
I did more or less the same measurements, and in order to avoid the
uncertainities due to the jitter present in the GPS 1pps output, I
divided the 10MHz rubidium output to 1MHz, and measured time intervals
usign 1pps as start and the divided output as stop.
David Kirkby wrote:
> 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.
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