> Isn't it possible that what's really happening here is
> that the DSP is interpreting the absence of signal as
> very weak signal and applying very high gain in order
> to optimize the signal applied to the input of the
> ADC? The net result is it sounds noisy but it really
> isn't. I think it might have been Grant who posted
> some info a coupla months back that did a great job of
> theorizing what is happening here.
Yeh, it was probably me feeling the side of the elephant :-)
I believe that's exactly what is happening. And the "proof", based on
my meager understanding, is that when an antenna or some RF
source other than kT noise is present, this "noise" business
vanishes.
What the radio does with essentially no signal, is immaterial to its
performance when there's something there (intelligence, band
noise, whatever).
If the threshold is set to the minimum value, and there is no signal,
the DSP gain stages are going to try to run wide open. Any random
stuff, kT noise, jitter, ertc. appearing at the ADC output is going to
be amplified, and will of course sound like a lot of noise. But it
sounds that way only because the DSP gain is very high, and
there's no signal to cause gain compression.
Grant/NQ5T
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