Abstract: An oscillator suitable for use as a local oscillator of high frequency apparatus comprises a voltage controlled oscillator, a reference oscillator, a phase detector for detecting the phase difference between the oscillation frequencies of the voltage controlled oscillator and the reference oscillator, means for filtering the output of the phase detector to produce a DC voltage and a phase synchronizing loop for feeding back the DC output of the low-pass filter means to the voltage controlled oscillator. Depending upon whether the oscillation frequency of the reference oscillator is maintained at a duty cycle of 50% or at a value other than 50%, the oscillation frequency of the voltage controlled oscillator is synchronized with an odd multiple or an integer multiple of the oscillation frequency of the reference oscillator when the oscillation frequency of the voltage controlled oscillator is varied forcibly.

Abstract: In a method of presetting a receiver of the synthesizing type wherein the ratio of frequency division of a frequency divider in a phase locked loop is set in accordance with the content of an up-down counter, a search signal and a write signal are generated for sweeping the up-down counter, the contents of the up-down counter are sequentially written in a memory device each time an intermediate frequency output is obtained, and the up-down counter is preset in accordance with a data read out of the memory device thereby enabling the receiver to receive the signal from a desired broadcasting station.

Abstract: A trigger signal for indicating the receiving point of a synthesizing type high frequency receiver including a voltage controlled oscillator is detected by a circuit comprising means for deriving an intermediate frequency signal from the received high frequency signal, a wave shaper for shaping the waveform of the intermediate frequency signal, a first monostable circuit connected to the output of the wave shaper and having a time constant larger than the width of the output but smaller than the minimum frequency spacing between individual stations, a second monostable circuit connected to the output of the first monostable circuit and having a time constant smaller than the width of the output of the wave shaper, and an AND gate circuit for producing a logical product of the output of the second monostable circuit and a sweeping clock signal.