RTL-SDR sample bit depth

Leif Asbrink leif at sm5bsz.com
Mon Mar 5 09:27:05 UTC 2018


Hello John,

> I'm looking at 192 kHz of spectrum in a 1024 bin FFT, so that's 187.5 Hz
> per bin.  Trying to understand what you said below, is it correct that I
> should view the bin width as the equivalent of the receive bandwidth for
> MDS purposes?
This would be the case if the FFT is un-windowed which it is
probably not. A window function will make the data points
go towards zero at the ends of the data block.
Have a look here:
http://www.sm5bsz.com/slfft/slfft.htm

The filter function that each fft bin represents can
be obtained by computing the FFT of the window function.
If you do not know it, you might guess that it is 300 Hz or so.

A better strategy is to select for example SSB mode with
a filter bandwidth of 1 kHz. Then measure the noise level
within the passband. Many SDR software have a true RMS
detector that would allow precise measurements.

73

Leif






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