In a message of Thu, 25 Feb 2016 05:15:58 +0100, Tom Theisen writes: >Could you please give me some hints on how I could implement this in >GNURadio? Modulation index would be nice to have, but I'm really after >the freq. dev.
Just a sketch of how I would do it: You need to find out the bandwidth of the modulate FM signal, as well as the maximum frequency of the modulating signal. So demodulate it, and average the spectrum of both the modulated and demodulated signal for a while (how long a while is will obviously depend on the signal. If it's a steady sine wave a while is a cycle, if it's a broadcast FM station without RDS and other subcarriers, probably a few minutes to get both speech and music). Once you have that, figure the bandwidth (bw) of the FM signal, and the maximum frequency (fmax) in the demudulated signal. The bandwith is (approximately): bw = 2*fmax + 2*dev so deviation is: dev = (bw - 2*fmax)/2 modulation index is just: h = dev/fmax HTH /Anders _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
