This filter for receiving audio in telegraphy was found in a magazine 73 for radio amateurs, in an edition of the 80s. The circuit is tuned to 700 Hz and has a 200 Hz bandpass.
This circuit appears in several versions on this site. It is designed to be used between the...
This circuit uses a piezoelectric tweeter to emit a powerful continuous sound above the audible...
This circuit is based on a Siemens S566B integrated circuit. The circuit is from a Radio...