This circuit was found in the January 1991 issue of Radio Electronics magazine. The circuit uses integrated circuits of the time and the coils depend on the tuned bands.
This instrumentation amplifier with differential inputs was found in documentation from the 90s....
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
Found in a 90s 303 Circuits, this circuit has an output power of 100 mW. L1 consists of 890 turns...