[time-nuts] G3RUH GPS Stabilized Oscillator

[Dr Bruce Griffiths]

Richard W. Solomon wrote:
> I built two of the GPS Stabilized Oscillator circuits (G3RUH as
> modified by N1JEZ). They seem to work, except that I still have
> not been able to confirm that the 10 MHz XO (FOX) is truly locked
> up to the GPS signal. I can verify that the GPS Engine is locked,
> but I still cannot prove to myself that the XO is locked.
>
> I made one up to lock up a 1 GHz PLO that I can use for calibration
> of my Service Monitor and the other to use as external references to
> a couple of EIP counters.
>
> Any thoughts or suggestions (other than using the services of NIST !!). 
>
> 73, Dick, W1KSZ 
>
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>   
Richard

You can always measure the frequency of the oscillator by dividing it 
down and using a time interval counter to measure the time from the GPS 
output pulse to the next rising edge of the divided down output.
If you know the oscillator frequency sufficiently accurately 
(sufficiently accurately that the number of divided down periods between 
successive PPS pulses is known to better than 1/4 of a  divided down 
frequency cycle) then you can unwrap the phase measurements and 
determine the actual frequency from the phase vs time plot using the 
technique used  in the picket fence technique detailed in:

/"A Method for Using a Time Interval Counter to Measure Frequency 
Stability"/ C.A. Greenhall

If you know the oscillator frequency to better than say 100ppm then 
divide it down so there are no more than 2500 cycles of the divided down 
frequency between successive GPS PPS pulses.

Bruce