Re: An enhanced demodulator for the NOAA APT satellites?
are you sure it is the same transmission repeated along in frequency? This seems to be a waste in a fairly constrained band. I am a total newbie in APT so I just went to Wikipedia (https://en.wikipedia.org/wiki/Automatic_picture_transmission) and read "The signal itself is a 256-level amplitude modulated 2400Hz subcarrier, which is then frequency modulated onto the 137 MHz-band RF carrier. Maximum subcarrier modulation is 87% (±5%), and overall RF bandwidth is 34 kHz." so it does not seem to be exactly as you describe. But maybe some specialists could give a better answer.