This circuit is intended to recover a very weak signal at a receiver, for example, a CW signal or a tone signal. The circuit is from a Popular Electronics from the 90s.
This signal generator found in Japanese documentation of 1973 uses an unusual integrated circuit...
This circuit is from a Texas Instruments manual from 1968 but can be applied to current controls...
We found this circuit in an 80s Intersil documentation. Modern equivalent operating systems can be...