Suggested by Siliconix in documentation from the 90s, this circuit can present gains of digitally selected by the input going from 1 to 1000. The circuit can be adapted to work as a shield.
This circuit makes use of a PLL 567 and the components must be calculated according to the desired...
The transmitter can be that of CB9574E. This receiver uses a PLL to directly trigger a sensitive relay....
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...