[time-nuts] Using cheap sound cards for measurements

[Bruce Griffiths]

Lux, Jim (337C) wrote:
>   
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Bruce Griffiths
>>
>> If the 2 signals are sampled at different times then there is
>> incomplete
>> cancellation of the phase noise of the offset oscillator.
>> This effect increases with the delay between the 2 samples.
>> In practice the interchannel sampling delay can be relatively long
>> (hundreds of microsec) with a low noise offset oscillator.
>>     
>
>
> Since the lowest sample rate contemplated (except for my $25 DATAQ) is 44 kHz, that's 20-25 microseconds maximum offset, even if you use different digitizers, once you've figured out the alignment (which you could do with a single sync pulse fed to all channels)
>
>
>   
You still need to use the same master clock for both channels to ensure
that the phase noise contributed by this sampling clocks largely cancel.

Bruce