Communication Receiver Front-End Filtering

COMMUNICATION RECEIVER FRONT-END FILTERING by A. B. Bradshaw In communication receivers, whether intended for general coverage or for ama- teur bands only, front-end design has changed considerably over the years. With the use of higher intermediate frequencies (IF) and the availability of high-frequency (HP) crystal filters, we no longer see the multiple banks of tuned circuits and multi- gang capacitors. Unfortunately, for most new develop- ments there is a price to pay: the reduction in pre-mixer selectivity means that any amplifier preceding the mixer must offer superlative performance in terms of inter- modulation distortion and cross modula- tion. If it does not, the user may get the impression that the receiver is full of sig- nals. The old saying that "The wider the window"s open, the more muck blows in" is very apt here. It was with these thoughts in mind that the writer has designed some general-pur- pose front-end filters for the amateur bands. If you need more protecti...