This circuit was found in a 1969 Motorola documentation. The FET admits an equivalent. The circuit has high input impedance and is powered by voltages from 6 to 30 V.
The circuit shown in the figure was suggested by National Semiconductor in its 1994 Linear...
The purpose of this circuit is to detect output signals from a transmitter for the frequency range...
This transmitter uses an electret microphone and has a few tens of meters in range. The coil L1 is...