This selectivity multiplier circuit for 455 kHz IF receivers was found in American documentation from the 1980s. The circuit requires a symmetrical power supply.
The figure shows how to use an LM3914 with a variable range moving point. The circuit has an...
This circuit was found in a 90s Popular Electronics. It uses a varicap that admits equivalents. The...
This circuit is from an Electronics Now from 1998 and can be easily assembled with other JFET...