[time-nuts] GPSDO question

[Hal Murray]

karl at lautman.com said:
> It has a couple of LEDs which allegedly indicate it's GPS locked and its
> accuracy is better than .05 Hz.

> 1.  I assume that .05 Hz quality spec is embedded in the GPS signal.  Is that
> correct?  If not, how is it calculated?

There is a key idea missing from that spec and question.  How long are you 
measuring/averaging over?

If it is actually locked, I'd expect the frequency to be correct and the more 
interesting specifiction would be the spectrum.


> The BK's frequency reference is a 1 ppm TCXO, but the counter only provides 8
> digits of precision when running on the internal reference;

1 PPM is only 6 digits.  The other 2 are "interesting".  They may be useful if the TCXO is stable - it lets you compare 2 sources.

You can calibrate the internal source by looking at a GPS.  Just measure the PPS or 10 MHz.  Then assume it is accurate and back compute what the internal reference frequency would have to be to get that answer.


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