narrow band IF strip - an IF amplifier/demodulator for amateur receivers

6-22 — elektor june 1980 narrow band IF strip Several things have to be taken care of first. The IF signal, which is produced by the front-end of the receiver, must be "purified" or "cleansed" of as much unwanted noise as possible so that only the pure IF signal is left. This is done with the aid of a filter circuit. The cir- cuit here uses crystals; which is known to be one of the best methods to achieve high selectivity. The filter circuit is designed for an IF of 9 MHz. An advantage is that use may be made of popular 27 MHz "3rd octave" crystals. These are easily obtainable and what"s more, at a reasonable price. The pure 9 MHz signal could be ampli- fied and then demodulated, but it is better to have an intermediary stage and derive a second IF with a much lower frequency (130 kHz) from the 9 MHz IF. In this way a "double" super heterodyne circuit is achieved with two narrow IF skip an I F amplifier/demodulator for amateur receivers An amateur receiver for the two metre (144...