Bob Poortinga wrote:
> Joe Taylor K1JT <joe@...> writes:
>>As it happens, there is one way in which poor sound cards can adversely
>>affect WSJT signals. It's not S/N, but rather inaccuracies in sampling
> Doesn't sampling jitter also introduce noise? Wouldn't a highly-stable
> sampling clock produce a lower noise floor resulting in better decodes?
Yes, but for any plausible amount of jitter that noise will cause
negligible degradation of the WSJT audio signals sent from your radio to
the sound card input.
The "inaccuracies in sampling rate" that I mentioned are not jitter, but
rather a sampling rate that is constant but offset from the nominal
value by a significant amount. WSJT always requests a sampling rate of
11025 samples per second. The actual sample rate can be somewhat
different. Some recent sound cards are "off" by as much as 75 Hz,
sampling at about 11100 Hz instead of 11025. If uncorrected, this means
that the WSJT tone spacing will be off by about 0.7% in both time and
frequency, causing a loss of sensitivity up to about 2 dB.
The next WSJT version to be released will have the ability to correct
for errors in sound card sample rates.
>>The Rig Expert may be a convenient way to do your radio-computer
>>interfacing, but it will NOT gain you 10 dB (or even 1 dB) in detecting
>>weak meteor pings or EME signals.
> Thanks, Joe, I was simply looking for a definitive answer in response to
> the claims of others.
> 73 de Bob, K9SQL
Happy to help!
-- 73, Joe, K1JT