Detector with ferrite core coils

[Gervm]

If interesting Russian search head (look picture higher). TX coil - about 1000 turns of 0,35 wire on the steel core and two RX coils without cores. Each RX coil consist of 3500 turns of 0,1 wire inductance 400mH R-1400om. Betwin coils were two little cores for reducing leftover signal. BallanIce betwin TX and RX must be better than 50 mV (0-50). This unballance reduces by compensator of signal. In army I operate so units and say that one from three was made good (for so simple circuit). It had 5 thansistors (2 of them were in oscilator). Some units were bad and unstable but I think it was result of bad assembly and bad parts. They use bad germanium transistors and coil capasitor had paper isolation betwin foil...