This is a fun blog by David from Rowetel who has been using his tech to track down “a troll who is annoying us on our local repeater.” That’s an interesting problem and requires interesting solutions.
The trick is to get signals from two antennas into the SDR, in such a way that the phase difference can be measured. One approach is to phase lock two or more SDRs. My approach is to frequency shift the a2 signal, which is then summed with a1 and sent to the SDR. I used a Minicircuits ADE-1 mixer (left) and home made hybrid combiner (centre)