MICRO FM Bug

  
The circuit consists of three stages, an electret microphone, an audio amplifier and an RF oscillator. The electret microphone consists of only two parts - a FET transistor and a plastic diaphragm. There is nothing else inside the case. The 3-leaded FET has an input, output and earth lead. The mylar diaphragm has been permanently charged with a static charge and this is one of the secrets of the operation of the microphone.
MICRO FM Bug - schematic

The FET transistor has a very high input impedance and because it is an active device, we call it a stage. The gain of this device is extremely high because it is able to amplify the charges from a charged surface to produce an output in the millivolt ra



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