Re: An enhanced demodulator for the NOAA APT satellites?

Siegfried Jackstien
 

he sees the "sidebands" as 20 or 24 carriers in parallel ...

the apt signal is

one tone only (the 2k4 subcarrier)

but if you frequency modulate a signal with a single tone .... you see a main carrier ... and lots of signals left and right from it (the fm sidebands)

those are normal ... and there is not the signal send out several times in parallel

dg9bfc sigi

Am 09.10.2019 um 15:45 schrieb Edouard Griffiths:

Hello,

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.

Brgds,
Edouard.   

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