https://axleos.com/building-a-gps-receiver-part-1-hearing-whispers/
I decided to try my hand at decoding these GPS signals, guided by the vague end-goal of plucking out my position from peanuts. I learned that the GPS signals that facilitate our mapping apps are ever-present, around us at any altitude, in any weather conditions, at all times.
This sounds cool in the abstract, but the tangible reality is staggering. These signals are all around me as I write this. They're all around you as you read it. The world is soaked in these whispers, repeating themselves endlessly for anyone willing to listen.
You can find out exactly where you are, from thin air, anywhere at any time, by learning to speak the language of the electromagnetic waves flowing over your skin. These waves have been a constant and quiet companion for most people's entire lives.
[...] All that said, it's not as though there's a cacophony of navigation data swarming around you, deafening if you could just hear it. In reality, the GPS signals surrounding you are astoundingly weak. To take an analogy: imagine a normal light bulb, like the one that might be above you now. Pull it twenty thousand kilometers away from the room you're in, and have it flash, on, off, on, off, a million times a second. Imagine straining your eye to watch the shimmer of the bulb, two Earths away, and listen to what it's telling you.
[Ed's Comment: Links to subsequent parts of this series are included in the source article]
(Score: 2) by VLM on Thursday April 18, @04:22PM
If you recall the Iranians MANY years ago transmitted spoofed GPS signals to convince an American drone that it was putting along in the sky at full speed while it landed at an airfield in Iran.
GPS spoofing is "old" stuff.
What is new is the FPGAs and SDR transmitters necessary to do it has gone in recent years from "millions of dollars programs" to very serious hobbyist level.
Its the usual double edged sword just like weather service SAME codes where building a device that uses them requires building a test chamber holding a spoofing system, although lets be real probably 99 out of a hundred people who compile and execute that code are screwing around not really using it.