Found in a Popular Electronics from the 90s, this circuit is intended to measure the harmonic distortion of an audio signal. The circuit can be tuned between 970 and 1030 Hz.
With this circuit, signals in the range of 10 kHz to 150 kHz can be received at close to 4 MHz...
This limiting circuit with an operational amplifier has an adjustable cut-off point and can use...
Published by Philips in 1965 documentation, the sensor for this circuit is a common LDR. The...