Found in Maxim's documentation from the 90's, this circuit uses a component from the time and has its performance curve shown next to the diagram.
This VCA was found in the July 1988 issue of Radio Electronics magazine. It uses an OTA op amp and...
Found in US documentation, this circuit changes the waveform and phase of a sine signal. The...
Found in an American amateur radio documentation by the name of “antennascope” this circuit is...