[time-nuts] Beginners GPS locked frequency counter question

Jim Lux jimlux at earthlink.net
Sat Oct 31 13:12:50 EDT 2015

On 10/31/15 3:50 AM, Chris Wilson 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?
>     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?

you could probably get a DDS of some sort to take the high quality 10MHz 
and turn it into the clock frequency of your sound card. You'd need to 
figure out how to pull the XO off the board and feed an appropriate 
signal in.

There's a fair number of people interested in this, so I suspect someone 
has already done it.

The other approach is to replace the XO on sound card with a VCXO, and 
"discipline" it against the 1pps from the GPS.  It's a matter of using a 
different divisor than 10,000,000.

More information about the time-nuts mailing list