This 4-tube circuit was found on a Radio Craft from December 1945. The circuit has excellent sensitivity. Power comes from a power supply with a transformer.
This S-meter circuit was found in a 1976 publication. The circuit is used to measure the signal...
Several versions of this circuit can be found on this website. This makes use of FETs that can...
With the circuit shown in the figure we have a frequency modulation which is produced by a...