Found in Texas Instruments documentation from the 1980s, this circuit applies to digital signal transmission with FSK modulation. The circuit is slow, as it uses period components.
The amplifier shown in the figure is from the manual of linear integrated circuits from Analog...
It is the traditional version of a Galena radio with a germanium diode and a high impedance phone....
This circuit was found in a 1980s instrumentation publication and can be applied to virtually any...