[time-nuts] Beginners GPS locked frequency counter question

Bob Camp kb8tq at n1k.org
Sat Oct 31 09:13:28 EDT 2015


> On Oct 31, 2015, at 6:50 AM, Chris Wilson <chris at chriswilson.tv> wrote:
>  31/10/2015 10:46
>   I have a Racal counter locked to 1 MHz on its rear panel external
>   input socket from my Trimble Thunderbolt GPS. I derive the 1 Mhz
>   from a David Partridge divider board. If I also feed the counter
>   with the 10 Mhz direct output from the same GPS it reads one or two
>   Hz out. As I assume the counter is working purely mathematically
>   why would that be please?

Is it always out in the same direction ( = broken counter) or does it
bounce back and forth to each side of “correct” ( = noise) ?

>   As an aside, I work low frequency RF transmissions on 136 Mhz, and
>   very narrow bandwidth. Can a soundcard be locked to GPS instead of
>   its own internal crystal for precise frequency output?

Yes and there are threads on the list about doing this. The quick wrap up is:

1) Find the clock source (oscillator or crystal) on the sound card.
2) Pull it off the card and attach a cable.
3) Synthesize the correct frequency off of your GPSDO’s output (generally 
with some sort of PLL / VCO arrangement) 
4) Feed the signal into the cable to the sound card 


>   Thanks.
> -- 
>       Best Regards,
>                   Chris Wilson.
> mailto: chris at chriswilson.tv
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