Circuitry for the diversity unit in an fm receiver for a telephone system

Abstract

A circuitry in a diversity unit of an FM receiver for a telephone system having at least two channels for receiving signals, and at least one phase-lock loop. The signals received by the channels which possibly differ from each in amplitude and frequency. Each channel comprises a mixer and a band-pass filter for forming an intermediate-frequency signal. The phase-lock loop has phase-lock branches operably connected between each mixer of the channels which comprises a frequency-phase comparator. The phase-lock loop equalizes the channel signals in phase and amplitude. The phase-lock loop further has a summation circuit for adding the channel signals which have been equalized. The frequency-phase comparator has a single phase-lock branch exiting therefrom along with a voltage-controlled oscillator connected to one of the mixers of one of the channels. The voltage-controlled oscillator has a switch on an input side thereof. The switch are for disconnecting the input side of the voltage-controlled oscillator from the frequency-phase comparator of the single phase-lock branch and for switching the voltage-controlled oscillator to a fixed and preset reference frequency. Coupled to another of one of the mixers of another set channels is a fixed-frequency oscillator and a signal-level sensing circuit which, in an event of slow fading the other channel, inputs a separate signal to the switch means of the voltage-controlled oscillator in order to switch the voltage-controlled oscillator to the fixed reference frequency.