Radio receiver with switching circuit for elimination of intermodulation

Abstract

A radio receiver includes a first tuner, a first intermediate-frequency amplifier, at least two intermediate-frequency filters connected between the first tuner and the first intermediate-frequency amplifier and having difference frequency bands, a switching circuit for applying an output signal from the first tuner through a selected one of the intermediate-frequency filters to the first intermediate-frequency amplifier, an automatic gain control circuit for controlling the gain of the first tuner, a first phase-locked loop for enabling a local oscillator in the first tuner to oscillate at a frequency dependent on the frequency of a desired channel, a second tuner, a level detector circuit for detecting the level of an output signal from the second tuner, a second phase-locked loop for enabling a local oscillator in the second tuner to oscillate at a prescribed frequency, and a controller for controlling the first phase-locked loop to enable the first tuner to receive and issue a desired signal from a desired channel, for controlling the second phase-locked loop to enable the second tuner to receive and issue signals from the desired channel and other channels, for enabling the level detector circuit to detect the levels of the received signals of the channels, for selecting the one of the intermediate-frequency filters based on the detected levels of received signals, and for controlling the automatic gain control circuit.