dBFS vs Vertical dB Scale

[grege...@gmail.com]

The newer versions of gqrx have a vertical dB scale along the left side of the panoramic display, and they also have a horizontal dBFS bar graph in the upper right of the same window.  The two scales do not give me the same signal strength reading on a signal.  Could someone explain what the two scales are indicating, and which one might be more proper to use for comparing relative signal strengths?  I do realize that these are relative scales unless a calibration routine is done.

Thanks,

Greg Ella

AD0JP

[Alexandru Csete]

Greg,

Both the FFT and the signal strength indicator show the power in dBFS
- dB below full scale. The difference is the bandwidth. The signal
strength indicator bandwidth is set by the channel filter, e.g. 2.7
kHz for SSB, whereas the bandwidth on the FFT plot depends on the
sample rate and FFT resolution.

For instance, if your input sample rate is 500 kHz and the FFT size is
8192, then the bandwidth of each FFT bin will be 500000 / 8192 = 61
Hz. Then some additional processing is done to shrink the 8192 bins
down to screen resolution, but this is basically it.

This has been like this for the very early days of gqrx, so nothing
new in the newer versions :-)

Alex

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[grege...@gmail.com]

Thanks Alex!