User's Guide for Building and Operating Environmental Satellite Receiving Stations.If you're interested in reading more of the technical details of the APT signal, your two, primary documents are: That signal is then modulated onto a 137+ MHz signal using frequency modulation (FM) with a 17 kHz deviation. The imagery is bandwidth limited to 2080 Hz and amplitude modulated (AM) onto a 2400 Hz carrier with bandwidth of 4160 Hz. The Automatic Picture Transmission (APT) signal is an analog signal used to transmit low resolution imagery. Their set-up means that, aside from the computer required (which is now lessened to a Raspberry Pi, if you're so inclined), you can receive such signals for less than $50 in parts (SDR and antenna). These signals are meant to provide access to weather data for those with minimal access to equipment and budgets. There are currently (as of December 2020) three operational satellites that provide APT transmissions. Currently, NOAA operates a set of polar orbiting satellites that transmit both high resolution and low resolution (APT) weather imagery. TIROS-8, launched on 23 December 1963, added a continuous, analog video signal called "Automatic Picture Transmission" or "APT". Since then, new satellites have been launched to both augment or replace those that reached end-of-life.
It was the greatest April Fool's non-joke ever. NASA launched the first weather satellite, TIROS (Television Infrared Observation Satellite) into space on April 1st, 1960. You can frequency demodulate the NOAA APT signal, create a WAV file, then use Martin Bernardi's "NOAA APT Decoder" program to give you beautiful images.It will (if I understand it correctly) already control your RTL-SDR and audio card to process the data and give you beautiful, synchronized images. The Wxtoimg program can give you beautiful images pretty-much automagically.There are two straightforward methods if you just want an image. This makes them a perfect target if you want to try out using Gnu Radio Companion (GRC) on something a little different. These are the Automatic Picture Transmission (APT) signals.
Several of those transmit relatively low frequency (137 - 138 MHz) signals that contain low resolution visible and infrared imagery (roughly 4 km) of earth. The US' National Oceanic and Atmospheric Administration (NOAA) operates a fleet of satellites to look at earth's weather. I'm writing this article because I think it's fun. Gary Schafer, Blursday, Pandemic Quarantine Time, Still Probably December 2020
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