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24-03-2013, 07:48 PM

i'm intrested to do a mini project on listening bug...so can you please help me

05-10-2017, 11:31 PM

Please send dz in docentation process as introduction,components,working principle ,result,future scope

jaseela123d · 17-10-2017, 04:47 PM

The thing also known as the 'Great Seal failure' was one of the earliest listening devices (or "bugs") to use passive techniques to transmit an audio signal. It was concealed within a gift given by the Soviet Union to W. Averell Harriman, the United States ambassador to the Soviet Union, on August 4, 1945. Because he was passive, he needed electromagnetic energy from an external source to activate and activated, is considered an ancestor of radio frequency identification (RFID) technology.

A concealed listening device, more commonly known as a bug or a cable, is usually a combination of a miniature radio transmitter with a microphone. The use of errors, called annoyances, is a common technique in surveillance, espionage and in police investigations. An error does not have to be a device designed specifically for spying. For example, with the right equipment, it is possible to remotely activate the cellphone microphone, even when there is no call, to listen to conversations in the vicinity of the phone.

Principles of operation

The Cose consisted of a small capacitive membrane connected to a small antenna of quarter of wavelength; It had no power supply or active electronic components. The device, a passive cavity resonator, was activated only when a radio signal of the correct frequency was sent to the device from an external transmitter. This is currently referred to in the language of the NSA as "illuminating" a passive device. The sound waves (from the voices inside the ambassador's office) traversed the thin wooden case, hitting the membrane and making it vibrate. The movement of the membrane varied the capacitance "seen" by the antenna, which in turn modulated the radio waves that beat and were retransmitted by the Thing. A receiver demodulated the signal so that the sound picked up by the microphone could be heard, just as an ordinary radio receiver demodulates radio signals and emits sound.

The Theremin design made the listening device very difficult to detect, because it was very small, had no power supply and no active electronic components, and did not radiate any signal unless it was radiated remotely. These same design features, along with the overall simplicity of the device, made it very reliable and gave it a potentially unlimited operational life.

Technical details

The device consisted of a 9-inch (23 cm) long monopole antenna (quarter-wave frequencies for 330 megahertz (MHz), but capable of also acting as half wave or full wave, the counts differ): a straight bar , led through an insulating bush into a cavity, where it was terminated with a round disc which formed a plate of a condenser. The cavity was a round and high Q silver plated "pot" with an inner diameter of 0.775 in (19.7 mm) and approximately 11/16 in (17.5 mm) long, with an inductance of about 10 nanohenry. Its front part was closed with a very thin conductive membrane (3 mil, or 75 micrometers) and fragile. In the center of the cavity was a flat-shaped funnel-shaped tuning post with its adjustable top to allow the distance between the membrane and the post to be fixed; the membrane and the post formed a variable capacitor that acts as a condenser microphone and provides amplitude modulation (AM), with parasitic frequency modulation (FM) for the re-radiated signal. The post had machined grooves and radial lines on its face, probably to provide airflow channels to reduce pneumatic damping of the membrane. The antenna was capacitively coupled to the pole through its disc-shaped end. The total weight of the unit, including the antenna, was 1.1 ounces (31 grams).

The antenna length and cavity dimensions were designed to make the retransmission signal a higher harmonic of the illumination frequency. The original device was placed with the can under the eagle's beak on the Great Seal presented to W. Averell Harriman (see below); the beads differ in whether holes were drilled in the beak to allow sound waves to reach the membrane. Other sources say the wood behind the beak was not perforated but thin enough to pass the sound, or that empty space acted as a sound box to concentrate the room sound into the microphone. The frequency of illumination used by the Soviets is said to be 330 MHz.

It can be understood in the following video:

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