so using the FFT output. The FFT output is in dBm (log10),
so has to be converted back from dB using pow(), averaged
and then converted back to dB using log10. This is trivial,
doesn’t use much CPU at all.
Averaging across frequency or time? Across
frequency summation is perhaps closer, particularly if you
presume it's all noise and simply add power per bin. But with
coherent sidebands on a signal you can get surprised simply
adding power I suspect. Alas, I do not KNOW that. I figure
it's easier to do the I^2 + Q^2 operation on the IF before the
demodulator. With that signal and something a bit like your
noise averaging the signal strength reading and noise reading
could actually help you know if there is enough signal to
expect your demodulator to provide something understandable,
especially for digital modulation schemes. (I'd take your
minimum 10% data, sum the powers (I^2+Q^2) in each bin, divide
by number of bins, and multiply back by number of bins in the
filter bandwidth to get the noise power estimate. That last
could probably be reduced to something close to a constant
multiply operation.) This makes WGN environments quite
predictable. Other environments suffer in comparison. So if
the calculation above gives too low an SNR, or value converted
to Eb/N0 is too low, then you know a
digital mode is not even worth trying. Of it is high enough
you know you have a sporting chance.
On 20210705 22:46:33, Simon Brown wrote:
FM power is always constant, this *could*
be an area for an averaging signal meter.
I’m slowly losing the will to live 😊 .
Simon Brown, G4ELI
[Edited Message Follows]
[Reason: Initial send occurred for seemingly no reason.]
I probably misspoke at some point if/when I said BCFM
carrier is always the greatest power anywhee in teh
passband, so I retract any such statement.
However, that statement does hold true for BCAM, so I've
captured a video of SDRC's S-meter reporting on a BCAM
Several key observations:
1) The carrier is very steady.
2) The modulation varies greatly.
3) the passband is intentionally varied between 2.5k and
4) The S-meter never varies at all (at least not more than
.1dB in any direction).
5) The S-meter is reporting ONLY the peak signal detected
anywhere in the passband, nothing more and nothing less.
So tell me where Simon gets it wrong.
Nevermind, that's a loaded question...Simon gets it right.
I'm done here,