Look what followed me home from that ebay. Original early 1950s AN/APX-6 Identification Friend or Foe transponder. These were using during the Castle nuclear tests as well as in many thousands of aircraft, with a base station mounted on the X band radar systems. In the late 1950s, many were bought as war surplus by radio hams and converted to the 1.3 GHz/23 cm band. It makes over a kilowatt from a pulsed disc-seal triode and has a radioactive T/R switch and three explosive Destructors