This circuit was found in a 1969 US documentation. It provides a signal that can be externally programmed as suggested circuits. The circuit can be used as a shield.
We found this 4-transistor receiver for the AM MW range in a 1960 transistor manual from Sylvania....
This 16-bit circuit was found in a 2005 Linear Technology application manual. The circuit uses...
The circuit is from an English publication from 1970, but it can be assembled with more modern...