Chapter 5 Listening to Satellites

Explore Software Defined Radio — by Wolfram Donat (22 / 30)

👈 Things to Try | TOC | Hardware 👉

Being able to tune into NOAA satellites while they pass overhead and download the images they’re broadcasting is probably one of the coolest things about using an SDR setup. It’s old-school technology that’s been around since the 1960s but is now becoming easily accessible to hobbyists and enthusiasts, thanks to the SDR dongle and the software that you’re now familiar with.

NOAA currently has quite a few weather satellites orbiting the Earth, keeping track of data worldwide, but there are only three that are broadcasting signals that are easy to receive. They broadcast around 137 MHz, and the signal can only be received when the satellite is passing overhead. Due to their orbital parameters, you can download the satellite’s transmission and decode it about twice a day, depending on where you live.

The satellites — NOAA-15, 18, and 19 — were launched in 1998, 2005, and 2009, respectively. They each broadcast a signal called Automatic Picture Transmission, or APT. APT was developed in the 1960s and is composed of two image channels, telemetry, and synchronization data, all transmitted as one horizontal scan line. You can use one of the programs we’ve already installed and used, GQRX or SDRSharp, to tune into each satellite’s particular frequency. You can then either record the transmission and send the audio recording to another application for…