This circuit was found in a 90s Popular Electronics. The circuit uses components from that time, intended to receive signals in the range of 150 to 250 kHz.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...