A Shout From the Edge of Satellites


There are many (artificial) satellites orbiting the earth, some functional, some long dead and some that have broken free of their natural lifespan to come back to life and begin transmitting again. Many of these transmit their data, weather images for example, on the 136-138mhz band and can be listened to with a cheap USB Radio/TV receiver and Software Defined Radio application.

I’ve been using these tools, just to see what’s in the various parts of the radio spectrum (spoiler: noise, lots of noise) and was hovering just below 136mhz where I picked up a signal:

This is just one section of it (I recorded around 4) each of which begin with a small burst of white noise before playing through a regular square wave pattern (which, I assume, is used to set/show the data rate) and then the section of what sounds like data. The image at the top of this post shows an attempt to decode it as a weather satellite image with wxtoimg, but this doesn’t seem to follow through – you can see the sections split by the lighter bands (a noisy one, then a regular one).

There’s certainly data there, but working out how to decode it is tricky. I’m going to approach it as if it’s using Manchester encoding to begin with, working from the square wave as the data rate, and see where that takes it.