In Part 5 I described my experiments using an 80cm parabolic dish fed with a short yagi as an uplink antenna. The performance was okay but not stunning. My next idea was to try feeding the dish with a 2.4GHz patch antenna. I ordered the Furious FPV “two slices” patch antenna as it was circularly polarised and quite cheap. Although the QO-100 satellite uplink requires right-hand circular polarisation, I chose the left-hand version since the, when reflected by the dish, the polarisation is reversed. This particular antenna is actually marketed for controlling FPV (first person view) drones. Unlike typical amateur patch antenna designs, this has two thin PCBs separated by an air gap. I am assuming that the back PCB is a groundplane.
Installing the Patch FeedThe patch antenna was clearly not going to be weatherproof, so I fitted it inside a small ‘tupperware’ container. This would also prevent detuning caused by water droplets. The photos below show the patch antenna before and after mounting in the plastic container. I also included an SMA-N type adapter as I was planning to use an N-type connector on my feed cable.
TestingInitial performance was disappointing, but signal strength was improved by some adjustments to the dish elevation. So now my CW signal results in a solid S8 signal coming back from the satellite, as measured on the downlink SDR receiver at Goonhilly. This is sufficient for solid CW contacts through the satellite, but not great for SSB working. Because of the high noise floor, an S9 signal is really needed for comfortable reception of SSB signals. When I tried out the system early this morning the signal strength was a lot lower than usual. I noticed that the plastic housing for the patch feed was covered in condensation as there has been a heavy fog today. The signal strength returned to normal when things dried up a bit.
EvaluationThe patch feed gives a clear improvement compared with the short yagi. However, with my current setup, SSB operation is still not practical. Also, the patch feed is rather flimsy and could be better engineered. I am planning to combine the 2.4GHz patch feed with a 10GHz LNB so that I have full transceive operation, so this would be a good time to re-engineer the patch feed.
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