[time-nuts] First success with very simple, very low cost GPSDO, under $8

Hal Murray hmurray at megapathdsl.net
Wed Apr 9 18:18:11 UTC 2014

> Actaully I don't care much about an "off by one" count because the problem
> is corrected in the next second.  If I happen to miss a count one second the
> very next second this shows up as an extra count.    I notice that something
> like this happens every few hundred seconds. 

I think you can turn that into a feature.  Suppose you start with the 
DAC/OCXO running at exactly 10 MHz, and the phasing such that you are right 
on.  Due to noise, the last count will be early and get counted half the 
time.  The other half of the time, it will be late and get counted in the 
next second.  So if you don't see that sort of noise occasionally, you know 
you are drifting off from a phase that was "right on".

Have you calibrated the DAC yet?  If you bump it up by 1 count, how long does 
it take for the OCXO to drift by a cycle?

Another low cost way to get better resolution would be to use 2 counters and 
a delay line.  Pick the length of the delay to be well above the noise level.

These are my opinions.  I hate spam.

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