This circuit was found in the April 1978 Radio Electronics magazine. The power supply must be symmetrical, and the maximum operating frequency is around 100MHz.
This is the receiver for the previous transmitter. The microphone is of the high impedance...
This amplifier, found in a 1980s documentation, should be powered by a symmetrical source. Modern...
The operational amplifier used in this circuit from a 1970s publication is no longer easily found...