Of coarse, if you know the transponder was ahead of you you would only need two antennas to establish to vector to the signal.
Or, even simpler still, a directional antenna (yogi) pointed out the windshield of the plane, rotate the antenna with some means to measure signal strength of the transponder signal. Sounds very crude, but it could work. How do you think they find those radio collars/tags they attach to wolves, bears, sharks, etc.
Of coarse, if you know the transponder was ahead of you you would only need two antennas to establish to vector to the signal.
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Commercial transponders operate on 1090 MHz ,, sounds familiar? FM radio operates on 88-108MHz but I believe a 10X signal would bleed through and make a whine so the transponder is conveniently just above 10X the top of commercial FM ... Could a manual tune (non-electronic) FM radio ,, a cheap $10 one ,, be tuned above 107.7 to 109.0 and used to find a bearing to another craft? Just a thought .. old manual tune TV’s could tune that freq... it’s in the UHF band.. food for thought..
I personally believe that this had to be pulled off by a country and not a handful of people... only they would have the ability to allow the craft through active military radars and deny that anyone passed through ... I put my money on China ,, they want those embedded processor engineers for what they know of the exact design changed demanded by the NSA.