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 TTL circuit uses LED indicators and must be powered by a voltage of 5 V. The capacitor...
The amplifier shown in the figure is indicated for operation with resistive transducers such as...
This oscillator for frequencies up to a few tens of kilohertz was found in a 1970s documentation. The...