We use the FM Mod and Quadrature Demod blocks to modulate and demodulate GFSK packetized data. In the past, we have used sensitivity values for these blocks that were provided for us, but their meaning was opaque.
I did some digging in the list and the web and found two prevalent definitions for sensitivity from examples. Both definitions were consistent in saying that the Demod parameter 'Quadrature Gain' should be the inverse of the sensitivity parameter for the Mod block.
The competing definitions for sensitivity were:
1. sensitivity = (pi / 2) / samples_pr_symbol # from gnuradio/blksimpl/gmsk.py
and
2. sensitivity = 2 * pi * max_deviation / sample_rate # from gnuradio/blks2impl/nbfm_tx.py
In my own recent work, I have been using the second definition because it seems to work and it gives me control over the deviation (I define max deviation using modulation index and baud rate).
However, when I attempt to use 1/sensitivity for the Quadrature Gain of the RX, it does not seem to work, while altering the RX definition of sensitivity to be 1 / (2 * pi * max_deviation / baud_rate) does seem to work.
Am I missing something fundamental about how these parameters work?