Tuesday, February 2, 2010

Satellite Audio Analysis

In a recent posting to amsat-bb, I asked if anyone knew of a way to grab the loudest-frequency and s/n data from an audio stream, thus saving for further analysis the data that Spectran shows in realtime over its waterfall. It seems this isn't an easy question to answer, so I did some more digging and came up with the following candidates.

Sonic Annotator appears to create metadata on audio files, using the vamp plugin architecture. There is a libxtract library that can be used in this architecture to grab spectral peaks, their amplitude and frequency. Wiring all this together, one could get a bunch of spectral peak data from a satellite's beacon and correlate the data to real-time. Then, we can use the realtime info from that to generate az/el values for the satellite in question.

Now, we have the spectral peak info correlated with az/el, and we can plot the signal amplitude against the position of the satellite in the sky. All this works best with beacons that are always-on, like VO-52's, for example, but I think one could make it work with CW, too, or perhaps the FM from CO-66, received in CW mode.

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