AN/APX-6

The AN/APX-6 was a Hazeltine-manufactured Secondary Surveillance Radar (SSR) system, specifically an Identification Friend or Foe (IFF) transponder, introduced around 1947. Operating in the L-band (950–1150 MHz), also known as the D-band by NATO, it utilized the Mark V standard on a new frequency band, also referred to as the United Nations Beacon (UNB). The transponder could receive double pulses between 960 and 1150 MHz and respond with single or double pulses, enabling compatibility with the frequencies of the newer Mark X standard. With a peak power of 1 kW and an instrumented range of 150 nautical miles (278 km), the AN/APX-6 briefly became a standard transponder for many aircraft, including the Boeing B-52 Stratofortress and the Lockheed C-130 Hercules.

radartutorial.eu: https://www.radartutorial.eu/19.kartei/14.ssr/karte037.en.html