At some point I might add details about how to decode the Automatic Picture Transmissions from the remaining NOAA Polar orbiting satellites. My SDR software along with my hacked Pluto-SDR, along with the 2m AZ/EL tracking antenna (137ish MHz) decodes it using:
IQ stream -> Quadrature Osc/Tuning -> Wideband FM demod (48 kHz) -> rectify audio (abs)->Decimate and LP filter from 48 ksps to 1500 sps-> map to grayscale and display.
This is quite the simplification, but I wanted to get it down as a placeholder.
This is the output:
Sad thing about APT – NOAA/NASA is no longer putting APT transmission into it’s future polar weather satellites. What little I know, I believe it’s because most everyone now has access to an internet connection, thus the imagery can be downloaded directly from NOAA. So it’s fun to occasionally download an image, but I’m not spending any more time on enhancements.