Abstract: A radio frequency (RF) signal transmitter/receiver system comprises a pair of transmitter/receiver units. A microcomputer-based RF carrier detect system determines when an RF signal is present or absent. The RF carrier detect system is also responsive to noise interference signals at or near its currently-tuned receiving channel. In periods of inactivity, the RF signal receiver monitors its currently-tuned channel and upon detection of noise interference or upon a determination that the currently-tuned channel is occupied, initiates a fast scan operation to identify an unoccupied and relatively interference-free channel, and transmits a command to its paired transmitter/receiver unit causing it to tune to the newly-identified unoccupied channel.

Abstract: A microcomputer in a radio frequency (RF) signal receiver, such as a cordless telephone set, periodically samples a received baseband audio signal to determine its frequency content. The microcomputer uses at least one predetermined frequency threshold value, and determines that the RF signal is present if the output signal contains signals no higher in frequency the frequency threshold value, and determines that the RF signal is absent if the output signal contains signals higher in frequency than the frequency threshold value. The circuit is useful in either a base unit or a handunit of a cordless telephone set.