[time-nuts] Discussion of precise time and frequency measurement
Tom Van Baak
tvb at LeapSecond.com
Thu Jun 30 04:23:43 UTC 2011
For long-term tracking 60 Hz (or any audio timing signal)
with a sound card you don't need a high quality.
Either use the PC to timestamp receive buffers, or if you
have a 1pps handy, just feed your 60 Hz signal into one
channel (L) and the 1 PPS into the other (R).
Either way drift in the sound card oscillator is irrelevant.
With little effort you can track the 1PPS to within 1 sample
(about 10 us at 96 kHz), which is way more precise than
the average 60 Hz power cycle.
Essentially what you're doing then is using 1 PPS as your
long-term accurate reference and using the sound card
merely as a cycle counter. For this the cheapest possible
sound card will do the job.
As described a day or two ago even a clockless one bit
"sound card" works at 60 Hz., i.e., a serial port DCD pin.
So in spite of the allure of using a sound card, it seems
a serial port is even a simpler solution if all you want to
do is count and time cycles.
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