CODAR bistatic radar using LimeSDR

[David Lonard]

Hello everyone,

Here are some results from using the two coherent channels to receive a CODAR radar signal at 4.450 MHz about 50 km away from my house.

I'm using a pair of magnetic loop receiver antennas arranged orthogonally to capture signals arriving in different polarizations. This should allow me to see ordinary and extraordinary reflections from the ionosphere and cross correlate them. This is somewhat different from what others have done by comparing the CODAR signal against an idealized FMCW waveform.

The CODAR transmitter transmits a 100 kHz FMCW signal that I've cross correlated and then performed an IFFT to get the signal delay. May ordinary - vs - extraordinary signals arriving at different times are noted, as are some likely separations of the F layer of the ionosphere. Some short blips are also seen which I am guessing are from meteor reflections.

David

[David Lonard]

[David Lonard]

I tried out a CODAR signal at 24.550 MHz. Not sure where it is, but it produced some interesting delay data.

David

[David Lonard]

Here is some math regarding the IFFT.

I'm sampling at 2MSPS, so each horizontal bin represents a signal delay of 500 nsec, or 149.9 meters. With delays of ~50 bins, this comes out to 7.49 km difference in some of the X and O signal that I'm seeing.

As such, I'm looking at a highly magnified view of the ionosphere (difference between X and O signal paths) than others who are looking at a single channel compared with an idealized FMCW waveform.

David