Hi Chris,
On 10/31/2015 11:50 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?
Your assumption is wrong.
There is a +/- 1 error in counting cycles.
Also, if the start and stop does not derive from the same trigger,
differences in the triggers can result in a time-shift which bias the
value. Difference in delay for start and stop events in the counter also
produces error. Also, the white phase noise contribute.
In essence, a number of practical design limitations makes measurements
somewhat noisier and somewhat biased compared to what theory says. It's
important to understand these so that their effect can be estimated and
sometimes mitigated.
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?
There is sound-cards you can lock to a 48 kHz clock.
Cheers,
Magnus
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