I am trying to recover my 2FSK signal using an SDR. I have centered the SDR modem on the median frequency (the virtual carrier) and captured my signal via some 90 kHz bw modem. THis is the recording of it below. You can hardly make out the sine waves from it. I have highlit one such sine wave - 56 samples @ 2.048 MHz sampling rate = about 36.6 kHz, which is close to what I am emitting. Should the necessary modem's bandwidth be in this case 2 * 36.6 + 19.2 (baudrate) = around 90 kHz ?
I am getting pretty much the same results with a 200 kHz bw modem. However, with a 250 kHz modem the sines are much better. But not quite perfect, like in the picture below. Am I seeing this artifact because of my actual signal's BW being wider than the calculated BW and even wider than 250 kHz or is it something else that I am missing ?
edit 1 Previously the RTL AGC was turned on and the Tuner AGC turned off (with RF gain set to 48 - almost to the upper limit). The following two new captures are from 250 kHz modem with Tuner AGC turned on (the only difference from second capture above). Funny what I am noticing. Here how the beginning of the message looks like
and here is the end of it:
edit 2 MUch better looking now with AGC off. I had to turn off AGC to both RTL and tuner in order to be able to manually set it to a custom value. That custom value was the maximum: 49.6 db; my signal is pretty faint, At 16.6 db I was barely able to see it is there.