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KGB bug
Early USSR radio bug

At the height of the Cold War, the Russian Intelligence Agency (KGB) used a variety of methods and equipment for eavesdropping on conversations in hotel rooms, embassies, private homes, etc. The device shown below was made around 1964 and was one of the first transistorized bugs.

The image on the right show the Russian KGB bug. The device measures 75 x 23 x 10 mm and is housed in a metal enclosure. It has three contact pins to which the power supply and the antenna are connected. The large black circle at the left is front of the crystal microphone.

The electronic circuit is extremely simple and consists of just one (Germanium) transistor, a simple coil and a couple of passive components. The tuned circuit consists of an adjustable coil with four windings, and a large capacitive (crystal) microphone connected in parallel.
  
KGB bug held in the hand

As the bug is based on a free-running oscillator, it is rather unstable and sensitive to power variations. In order to reduce the so-called hand effect, the transmitter is built inside a metal enclosure. Furthermore, the frequency is adjusted by moving a (grounded) core towards the coil. As this core is grounded, a normal screwdriver can be used for the frequency adjustement at the side of the unit. The adjustment can be locked by means of another screw that is located at the top surface. Power is connected to the two-pin terminal at one of the short sides (right).


When picking up a conversation, the capacity of the crystal microphone will vary slightly, causing variations in the resonance frequency of the tuned circuit. This will effectively result in a Frequency Modulated (FM) signal. The KGB bug shown here was ideally suited for a wide variety of concealments, such as a piece of furniture (e.g. the leg of a table) or a decorative table piece. An external power source (e.g. a battery) was connected to the 2-pin terminal at the right, while a wire antenna was connected to the single terminal at the opposite side (above the microphone).

KGB radio bug KGB radio bug KGB bug held in the hand Antenna terminal Power terminals Frequency adjustment Interior of the KGB bug Close-up of the internal circuit
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KGB radio bug
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KGB radio bug
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KGB bug held in the hand
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Antenna terminal
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Power terminals
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Frequency adjustment
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Interior of the KGB bug
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Close-up of the internal circuit

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Crypto Museum. Created: Friday 29 April 2016. Last changed: Tuesday, 13 June 2017 - 07:06 CET.
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