This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
This circuit was found in a 1980s documentation. It decodes by identifying a certain frequency tone...
The purpose of this 2000 documentation circuit is to decode SSB (BLU) signals to be audible on...
This circuit was found in Electronics Handbook, Vol XIII 1993 and consists of a simple direction...