Abstract: An automatic frequency scanning radio receiver which includes a phase-locked loop frequency synthesizer serving as a local oscillator circuit and a scan clock counter circuit to produce a program input signal. The program input signal is supplied to a programmable divide-by-N counter of the frequency synthesizer, whereby the frequency synthesizer has its output frequency automatically changed in steps to automatically scan channels within a desired received frequency band. A detection circuit is provided for detecting a tuning of the radio receiver to a broadcast signal above a predetermined input level on one channel, whereby scan clock counting of the scan clock counter circuit, or the automatic channel scanning is interrupted when the radio receiver is tuned to such a broadcast signal.

Abstract: In a muting arrangement of a radio receiver using a phase-locked loop frequency synthesizer as a local osicillator, a detector detects an in-lock or out-of-lock state of the phase-locked loop through an output state of a phase comparator included in a feedback loop of the phase-locked loop frequency synthesizer, and a mute gate provided in a signal transmission path of the receiver is operated to mute an audio output when the phase-locked loop is out of lock. An indicator may be provided for visually indicating that the phase-locked loop is in lock.