This circuit rejects frequencies around 1 kHz and can be adjusted using C1. Equivalent operational amplifiers can be used, and the power supply must be symmetrical.
This circuit is used in transceivers, enabling input selection by diode switching through polarity...
This configuration was found in an American publication from the 90s. Operators admit equivalents just...
This circuit was found in an Italian magazine Elettronica Prática of 1977. The transistors can be...