Abstract: This invention provides a bandwidth switching circuit for an intermediate frequency amplifier stage in an FM receiver that insures clear reception of desired signals by automatically switching the intermediate frequency amplifier stage between the wide and narrow bandwidths according to the radio field conditions. The bandwidth switching circuit includes a detector for detecting beat components due to interference contained in received signals and a change-over switch for switching the bandwidth switching circuit according to signals detected by the detector, whereby the bandwidth of the intermediate frequency amplifier stage is automatically switched depending on whether the beat components are present or not.

Abstract: This invention provides a frequency-synthesizer type transceiver having a voltage-controlled oscillator and means for comparing the phases of mixed frequency, whereby the voltage-controlled oscillator is regulated by signals resulting from the phase comparison to generate a controlled frequency serving as the local oscillator frequency for transmitting and receiving. The frequency-synthesizer type transceiver further includes a means for selectively switching from the one carrier frequency to the other to differentiate the transmitting and receiving frequencies.