This variable frequency circuit was found in a Popular Electronics from the 90s. The circuit outputs to a small speaker and can be powered by voltages as low as 3 V.
Found in the September 1972 issue of Radio Electronics magazine, this signal injector is based on the...
This is a traditional configuration of a series regulator with zeners, found in a documentation from the...
This small pulse receiver had its construction described in a Radio Electronics magazine from...