This circuit has the intensity of the signals controlled by the light that falls on the sensor. Note that it is not a frequency-controlled oscillator. Equivalent transistors can be used.
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...