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The SSR radar at Mt. Majura

The other day I was up at the Mt. Ainslie lookout and while enjoying the view, I saw the RASPP radar at Mt Majura, spinning as usual. So I tuned my scanner at 1030MHz (the frequency used by an SSR radar to interrogate the planes) and I made a recording of it.

When I got home, I put the recording through < href="http://www.visualizationsoftware.com/gram.html">Spectrogram and I got the following snapshots:

Mt Majura rotation period

Here you can see the strong signal that is received every 3.6 seconds which happens to be the period of all AirServices RASPP radars. Then I zoomed in on one of these groups of pulses and I saw the following:

interrogation rate

In this picture you can see the groups of pulses of each interrogation. They are spaced about 3.3msec apart which implies an interrogation rate of about 300Hz. If I had a better A/D (faster) than my sound card, I should be able to zoom in even further and see the individual pulses.