Wireless FM Mic the sophisticated eavesdropper

 

I started my first project, the Wireless FM Mic, a sophisticated wiretapping device. This work was 17 years ago, when I was still a student, in 1994.

I obtained the circuit from MOP magazine at the time. I tried to assemble it several times, but it didn't work until the fourth time.

It was fun to eavesdrop on neighbors' conversations by inserting it into a crack in the wall of the neighbor's house to be tapped, then listening to it through an FM radio receiver in my own home.

This Wireless FM could also be used for communication, and eventually, the whole village could chat over the radio within a 500m radius.

With the microphone's extraordinary sensitivity, it was rightly called the Wireless FM Mic, the Advanced Wiretapping Device, as the title of the MOP magazine article suggests. The circuit is simple, consisting of just two transistors. The first transistor, a 2SC289, acts as an oscillator and also acts as a microphone amplifier.

The second transistor, a 2SC1675, acts as an oscillator amplifier or buffer. This wireless system only requires a 1.5-3 volt battery supply.

The complete circuit diagram is shown in the image below.

                                               Wireless FM Mic Circuit Schematic

Component List :
R1 = 1k
R2 = 47k
R3 = 150
R4 = 33k
R5 = 180
C1 = 222
C2 = 1uF
C3 = 102
C4 = 10p
C5 = 10p
C6 = 222
C7 = 103
Q1 = 2SC829
Q2 = 2SC1675
MC = Mic Kondensor
Koker 5mm
5mm Coil L1 Primary 6 turns Secondary 2 turns Here's the layout: