What kind of hardware is needed? Do you envision these techniques result in a opensource software usable by general public?
The broadband downlink signals I’m interested in require a bit more effort— I’m using a 75cm offset parabolic dish on an azimuth/elevation turret with some nice high-end servos w/ built-in 12-bit encoders. Up until yesterday, we could only capture 60 MHz of real-time bandwidth; but now we have the device we need to capture closer to the entire 2 GHz span of the 10.7-12.7 GHz downlink in one fell swoop.
With all that, I still only get about 11 dB of SNR. I’ve seen hints that I might be able to get closer to 20 dB, which I could trade off for a smaller dish.
Which actually begs the question, can you decode anything (e.g. satellite ID) from the downlink/idle signal? If not, how do you figure out which satellite a given signal came from?
My first guess would be that you can fit an orbit to the Doppler shift, find the closest TLE set from space-track.org, and assume that the signal came from that satellite. Then propagate the orbit to the observation epoch and that should give you a fairly accurate guess of the satellite's actual location. Or do you do something completely different?
I’ve been able to demodulate and reconstruct about 100 subcarriers’ worth of signal, but until recently I couldn’t record the entire bandwidth. Now we’ve got our hands on one of those awesome RFSoCs with 2 Gsps ADC, so it might be possible to decode more. But unknown error correction, bit interleaving, so it’s a tall order. We’d have to get lucky.
Some projects like othernet also tried this.
I imagine a selection of international news, weather warnings, etc. that everybody can receive.