Originally designed for WWV (Standard Time Station) signals, it lets 1 kHz tones pass by rejecting the 440 and 600 Hz tones emitted by the station. The circuit is from a 1964 Electronic Design.
This circuit was found in an American audio documentation from 1968. The configuration can be...
This converter uses an SG1524 integrated circuit, which is uncommon nowadays. The circuit is from...
This circuit was found on an 80's Ham Radio. The transistor admits equivalent. The circuit can...