Abstract: In a mobile radiotelephone system, N separate modulated carrier signals in N frequency channels are applied to a demodulating radio receiver which provides a succession of N different output signals each having idle and busy states. An idle and signal-to-noise detector monitors each of the output signals of the radio receiver. The detector provides a first logic signal when one of the output signals concurrently exhibits an idle state and has at least a predetermined minimum signal-to-noise level, and provides a second logic signal at all other times. A receiver switching circuit, in response to the second logic signal, causes the receiver to cyclically switch to each of the N frequency channels. When the receiver switches to a carrier signal which causes the detector to produce a first logic signal, the switching circuit causes the receiver to lock onto that particular carrier signal.