Comment on [FoAR] Foundations of Amateur Radio - The Art of decoding a signal. #podcast
kristoff@infosec.pub 2 days ago
I find urh a great tool … except when you have no idea what it is. I usually use inspectrum as a first tool to have a basic idea what the signal looks like. Based on that, I decide how to go further.
Inspectrum is an older tool and has less features then urh, but sometimes simplicity works better.
Kristoff ON1ARF
vk6flab@lemmy.radio 2 days ago
Very interesting! I’ve installed it and attempted to look at the mystery signal, but I cannot make
inspectrumshow anything other than red. I think it’s sampled at 225144, but that’s speculation based on the filename. Any thoughts?Source file: github.com/vk6flab/signals/tree/main/recorded
kristoff@infosec.pub 2 days ago
I used inspectrum mainly with raw IQ-files from gqrx, so the c16 format is indeed correct.
For me, the great thing about the tool is that it is very visual. (*)
It allows you to get an idea what kind of signal you are looking at (on-off, FSK, PSK, …) and get a rought idea about timing. That then gives you information to better apply the proper filtering in urh and work from there on. It also allows you to see any “abnormallities” … e.g. I once came across a signal that sounded to be two-tone FSK, but after closer investigation, you could see that the two tones overlapped (in the time domain).
Concerning the bitstream you demodulated, I am not at all an expert in SIGINT, but I guess we can do some basic research like repeating pattern (that could indicated a start of frame), maximum number of consecutice all-0 or all-1 (that can indicate bit-stuffing) etc. The problem with unknown digital is that the number of variations of different processing-techniques is almost infinite: scrambling (not encryption, but scrambling) , FEC, …
(*) The visual element of inspectrum is the reason why I use it in a workshop I give. The workshop I do is similar to the one done by Mike Walters that is on youtube: www.youtube.com/watch?v=tGff31uGXQU
vk6flab@lemmy.radio 1 day ago
Thank you, that link was very helpful.