I found this circuit in a documentation for radio amateurs from 1975. The FET could be the BF245. The circuit works in the range of 40, 80 and 160 meters of radio amateurs.
The circuit suggested by National Semiconductor mows signals from a peak determined by the...
This 90's project shows how to use an old cassette recorder to practice telegraphy. In position A of the...
This circuit from Radio Electronics magazine, March 1994 edition uses two LM388 bridged, providing a 4...