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Welcome to the FM wiki!
The FM transmitter and receiver are based in the information presented for nccgroup for details between From Baseband to bitstream. The .pdf document is presented in the page:
https://cansecwest.com/slides/2015/From_Baseband_to_bitstream_Andy_Davis.pdf
The calculations are based in the Discussion Forum of Signal Processing in GNURadio (http://gnuradio.org/redmine/projects/gnuradio/wiki/SignalProcessing). For FSK modulation parameters normally appears like: sensitivity, gain or modulation_index.
sensitivity= (pi* modulation_index) / (samples_per_symbol)
gain = samples_per_symbol / (pi* modulation_index)
modulation_index = deviation / (baud_rate / 2)
Deviation refers to difference between 1 and 0 representation in terms of frequency (Delta f)
Using octave and gnuradio functions
filename = 'RF12B.dat';
f = fopen(filename, "wb");
fwrite(f, x, "char");
fclose(f);
In the implementation the block GFSK modulation generate different samples to the receiver, so is not coherent with the transmitter.
The RXDigital.grc works both with the sending data in RF12B module and with the sending in the N210 module