A duplex FM communication transceiver 10 is disclosed in which a modulated transmit carrier signal is utilized as the receiver first mixer (32) injection signal. The receiver portion of the transceiver comprises dual conversion circuitry, and the transmit information signal used for modulating the transmit...http://www.google.ca/patents/US4520474?utm_source=gb-gplus-sharePatent US4520474 - Duplex communication transceiver with modulation cancellation
