Radio Circuit Diagrams

FM Bugger Circuit

We all know that a FM Bugger is a device that sends information from one person to another in a distant location. Normally, bugger is used to determine a person’s status, such as where he is going, what he is talking about, and so on. Although it is illegal, the majority of spy agencies employ this flaw. This is a simple circuit that allows you to listen to another person’s talk over a great distance using a standard FM radio set. This FM bugger circuit is kept in the room where the conversation is to be heard. This dialogue can be heard on a regular FM radio set.

FM Bugger Block Diagram:

FM Bugger Block Diagram

The message signal or conversation signal is modulated using the carrier frequency generated by the tank circuit, as can be seen in the block diagram. The transistor modulates the message and carrier signals before transmitting the modulated signal through the antenna. The reception antenna receives the modulated signal and sends it to the FM radio, where the user can listen to the discussion. In order to receive the signal from the transmitter, the user must modify the receiver frequency in the radio.

FM Bugger Circuit Diagram:

FM Bugger

FM Bugger Circuit Explanation:

  • The circuit uses analogue modulation in which the carrier signal is applied continuously to the message signal. Here, in our circuit, the conversation of people is received by the MIC and give to the circuit is modulated to the carrier signal and transmitted.
  • There are various types of analogue modulation, including amplitude modulation, which includes single side band (SSB) and double side band modulation, and angle modulation, which includes frequency modulation and phase modulation. FM modulation is employed in this circuit. The carrier signal’s frequency is modulated according to the modulating signal’s instantaneous amplitude in FM modulation. When opposed to amplitude modulation, normal FM radio uses this sort of modulation to convey their messages. Frequency modulation has a higher throughput and efficiency.
  • MIC is placed in the room in which you want to listen to the conversation of the people and MIC will decode the conversation in to the signal which is given to the capacitor C1 where C1 is used for removing the noise in and turn on the transistor.
  • The tank circuit (capacitor C6 and L1) which produce the carrier signal for the conversation or message signal, the transistor will amplify the both the signals and send to air through the antenna. The capacitor C4 is used to remove the noise in the transmitted signal.
  • The capacitor C6 is variable because you can adjust the capacitor for producing your own carrier signal. Remember carrier signal should be in range of 88 to 105 MHz so that FM radio receiver set can receive your transmitted signal.
  • The FM radio receiver set is adjusted your frequency for listening to the conversation.


  • You can make L1 using about 25cm length of 25SWG wire. Wrap the wire around a cylindrical object of 6mm diameter and take it out after eight turns.
  • The transmission area range is around 100 meters.
  • Check whether the oscillator circuit is working properly or not before transmitting.
  • You can use a dipole antenna for transmitting the signal to increase the range of the transmitter.
  • Circuit operating voltage is around 3V, you can use a battery of 3V or normal DC supply as the power supply.
  • For better working use the PCB board for soldering or connecting the components in the circuit.
  • This circuit can be used in offices, colleges or any where you want remember bugging is illegal.


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