Found in American documentation from the 1980s, this circuit can be designed with equivalent components. The microphone can be of the piezoelectric type.
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This circuit was found in Signalite documentation from the 1960s. The circuit uses a pulse...
This low-pass filter was found in Intersil documentation from the 1980s. The circuit makes use of...