Air-to-air ranging system

Claim 1

IN A TRANSPONDER SYSTEM: AN ANTENNA; TRANSMITTER MEANS COUPLED TO SAID ANTENNA AND INCLUDING A MODULATOR AND A LOCAL OSCILLATOR; A RADIO RECEIVER OF THE SUPERHETERODYNE TYPE INCLUDING FIRST AND SECOND RADIO FREQUENCY TUNABLE CIRCUITS COUPLED TO SAID ANTENNA, A MIXER COUPLED TO SAID TRANSMITTER AND TO SAID RADIO FREQUENCY CIRCUITS, AND AN INTERMEDIATE FREQUENCY CIRCUIT COUPLED TO SAID MIXER; MEANS COUPLED TO BE ENERGIZED FROM SAID INTERMEDIATE FREQUENCY CIRCUIT OPERABLE TO GENERATE AND TO APPLY AN INTELLIGENCE BEARING SIGNAL TO SAID MODULATOR; MEANS TO TUNE SAID RADIO FREQUENCY CIRCUITS AND SAID TRANSMITTER WHEREBY SAID RADIO FREQUENCY CIRCUITS ARE RESPECTIVELY TUNED TO FREQUENCIES WHICH DIFFER FROM EACH OTHER BY TWICE THE INTERMEDIATE FREQUENCY OF SAID RECEIVER AND SAID TRANSMITTER IS TUNED TO A FREQUENCY BETWEEN THOSE TO WHICH SAID RADIO FREQUENCY CIRCUITS ARE TUNED; MEANS TO RENDER ONE OF SAID RADIO FREQUENCY CIRCUITS INOPERATIVE WHEN TUNED OVER A FIRST FREQUENCY RANGE; MEANS TO RENDER THE OTHER OF SAID RADIO FREQUENCY CIRCUITS INOPERATIVE WHEN TUNED OVER A SECOND FREQUENCY RANGE; AND MEANS TO REVERSE THE ORDER IN WHICH SAID CIRCUITS ARE RENDERED INOPERATIVE TO THEREBY PERMIT IMAGE MODE RECEPTION IN SAID RECEIVER.