This circuit was found in specialized microwave documentation from the 1960s. The circuit makes use of a varicap, and the transistor is a microwave type.
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...