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by greatartiste
1877 days ago
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Thanks for your post. I'm aware of Jindalee and the Russian OTHRs which claim to detect aircraft (and I believe the claim) but they are very different from WSPR. My station transmits 10 watts (and that's on the high side for WSPR) into an omnidirectional wire antenna. Some WSPR stations use directional yagi antennas but that information isn't contained in the WSPR data. A WSPR transmission lasts around 1 minute 50 seconds but the frequency shift/signal strength is only calculated the once during that transmission (not sure if by averaging). A transmission has to start within a second of the start of an even minute. Some stations are GPS locked but I just click the PTT on my radio to start the transmission while looking at the time on my digital atomic receiver clock. In answer to your questions some WSPR stations transmit every 2 minutes while others like mine only transmit once or twice an hour. |
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I'm guessing each station would need to lock its carrier to GPS and transmit as often as possible (10W would probably be okay with lots of stations). Similarly receiver local oscillators would need to be GPS locked (+/- 1ns?) and the receiver be coherent. Processing would need to be based on the raw stream of samples, but with a 6Hz bandwidth one could get away with a sampling rate of about 10 samples/s (Nyquist + a reality factor), each sample being a pair of 16-bit I/Q components. The low bandwidth might limit resolution. The signal processing would be the fun bit. Can all those receivers and transmitters be synthesised into one big array? Could the processing could be done in a distributed manner? Lots of interesting problems.
Apart from being an OTH radar, such a system would be the mother of all ionospheric sounders, as the main difference between a radar/sounder/communications is which features one chooses to extract from the received signal.
Is passive radar a thing in the amateur scene?