MICRO FM Bug

Posted on Nov 6, 2012

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.

Click here to download the full size of the above Circuit.

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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