GRAVES is a CW radar transmitter located in Dijon, France. Most of its energy is transmitted in a southerly direction and at an angle of around 20 degrees above the horizon. To listen to the echos from Graves I point my 4 element yagi in roughly a south east direction, I rotate it to use V-polarisation (the general consensus is that V-pol is better than H-pol - at least for meteors) and then feed that into my rtlsdr receiver (with a pre-amp to get over the cable run). The antenna is balanced on my wheelie-bin to give it around 1.5m above the ground - hardly an optimum antenna position. The receiver is tuned to 143.05MHz and a waterfall plot is created showing Doppler against time. Most of the time only noise is recorded, however about every 30 seconds or so a 'ping' will be heard from a meteor. Last night I listened when ISS was over Spain/France which meant that it should be illuminated by GRAVES and recorded the signal, shown below:
I've added some scruffy annotations below:
The Doppler signature from ISS is clearly visible along with a number of meteors and possibly a plane. (I'm not totally convinced that its a plane - the rate of change of Doppler is a lot to be explained by just a change in geometry). Anyway, some interesting results and a number of avenues for improvement:
- Change RTLSDR to use a TCXO to have some confidence in the absolute Doppler values measured.
- Use of multiple RTLSDR to measure returns from both polarisations to determine optimum - for all scatterers observed.
- Improve antenna location - move antenna to my roof when best polarisation determined.
Another object that I'm interested in receiving via the GRAVES transmitter is the moon - but I don't know how difficult that will be from my location and with my current antenna position.
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