US Patent 7230518 Multi-frequency security code transmission and reception

A system is disclosed including a transmitter and receiver for the communication of security codes which may be validated at the receiver to operate equipment. In one embodiment, the transmitter transmits a security code at two frequencies contemporaneously to the receiver which may receive both frequencies and resolve the security code therefrom. The receiver may lock onto one frequency when parts of a security code are detected to the exclusion of the other frequency. In another embodiment, the transmitter selectively transmits security codes at a default frequency which is selected because of a recorded count of prior apparent successful transmission.