Thanks for the informative reply. I think it's a fascinating system. On paper it could act as an OTHR if the signal processing was changed.
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.
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?