So, after looking for detectable data with lot’s of Python for some time - with no obvious result - I thought I should look more into the spectral analysis. So I got me that GNU Radio Block to read the file after after some arguing with cmake over failed dependency checks, I whipped up a very very simple GNU Radio Graph which reads from the file and dumps it with no post-processing to a FFT Waterfall Sink:

First FFT Waterfall diagram

Woohooo! OK, let’s quickly discuss what we see here.

  • We’re seeing a signal in the middle - the center frequency - which is usually an artifact from the local oscillator. It’s not really “real” in the strict sense. At least with my lousy setups…
  • What looks real, are the two bright signals about .5 kHz up and down the main (perhaps fake signal). But I can’t make out any details here. Do not forget, this many minutes long transmission has been compressed to this tiny picture.
  • What is odd are the strong signals +- 8 kHz up and down of the center frequency. The bandwidth is just way to high to be “just” harmonics.
  • We can also very vividly see how the center frequency drifts - this is owed to the Doppler-effect - it was sent from a spacecraft orbiting Mars, Mars is orbiting the Sun, it was received on Earth which is rotating around it’s axis and Earth is also revolving around the Sun. So it’s not surprising that the differences in relative velocity make the signal drift.

The GRC Graph is a pretty simple one, look:

GNU Radio Graph for displaying the recording

OK, now let’s zoom in a little. I added a Throttle, and for the fun, an audio sink, fiddled around with the FFT size, color scheme and whatnot, and this is what I got:

What the heck am I seeing? Are these figurines or is it just pareidolia

Download full image

I don’t know about you, but I think I’m starting to either suffer from pareidolia - I looked at FFTs for almost an hour - or can one really see figurines holding up their hands? :-)

I don’t know, but for tonight I call it a day.