This circuit can generate signals up to 100 kHz. Found in documentation from the 1980s, it makes use of operatives of the time.
The circuit below shows how to use an LM139 comparator or series equivalent as an amplifier. The...
We found this receiver circuit for modulated light in a 90s Popular Electronics. Equivalent audio...
The circuit was found in the February 1992 Radio Electronics magazine. The scale can be changed by...