VHF radio receiver input circuit - has primary oscillator working at higher frequency than received signal to generate intermediate frequency in mixer stage

摘要

The input circuit is for radio receivers working in the VHF band. The circuit overcomes problems associated with oscillator switching that can occur in television receivers and is based on the use of a primary local oscillator working at a frequency substantially higher than that being received at the aerial. The primary oscillator frequency is switched through the required range and generates in the first mixer stage an intermediate frequency by mixing with the output from a second and fixed frequency oscillator. A filter network is situated between the two mixers and it is designed to attenuate all but the desired frequencies.