narrow-band IF filter

EE 80 July/August 1986 155narrow-band IF filter Since good crystal filters are expens- ive, there is a constant search for (less expensive) alternatives. One of these is the ceramic filter, now widely used as IF filter in short-wave receivers. The somewhat poorer temperature characteristics of ceramic filters (as compared with those of crystal fil- ters) are normally not of much conse- quence. Numerous experiments have finally led to the circuit of Fig. 1, which uses five 455 kHz ceramic filters. As com- puter crystals can be obtained cheaply nowadays, it would also be possible to construct a similar filter with a number of such crystals. The result of our experiments is a 680p 220p I II-II 560p 1 1 II-11 680p 1 3300 * ■ 1n2 680P 680p 3300 * I_ ** I IITITITI 86442-1 3 dB filter bandwidth of about 800 Hz; the attenuation outside the pass-band is of the order of 60 dB. A possible application is its use in a receiver with variable bandwidth for SSB, AM, and FM operation. Another ap...