Abstract: A radio communication system having, at a local station: a transmitter adapted to transmit signals to a remote station with a predetermined carrier frequency; and, a receiver tuned to a carrier frequency of signals transmitted to the local station from the remote station, the carrier frequency of the signals transmitted to the local station from the remote station being different from the carrier frequency transmitted by the local station to the remote station during a normal mode of operation and tuned to the carrier frequency of the signals transmitted by the local station during a test mode of operation. With such an arrangement, the carrier frequency of the transmitter at the local station can be tested by a receiver at the local station without requiring the use a the remote station and without requiring additional equipment.

Abstract: Errors in communication of a bit stream of information are reduced by incorporating an error checking facility (e.g., parity checking bits) in the information, sending the information on two independent communication channels, and selecting the information sent on one or the other of the two channels based on an error checking analysis of the information sent on both of the channels.