Simple radio transceiver with high AM suppression - uses phase locked loop to control second IF mixers VCO

摘要

The radio transceiver has high AM suppression and simple construction, and has its second IF stage comprising a mixer, oscillator, band-pass filter, limiting amplifier and discriminator. To form a phase locked loop the output of the discriminator (10) is connected over a low pass filter (17) to the voltage-controlled oscillator's (16) control input. The discriminator is also supplied with a reference frequency (fQ) derived from a crystal oscillator (18) or by dividing the vco's output. The mixer (6) mixes the IF amplifier's output with the vco's and the result passes over the filter (8) and limiter (9) to the discriminator.