noise generator

(electronics) A device which produces (usually random) electrical noise, for use in tests of the response of electrical systems to noise, and in measurements of noise intensity. Also known as noise source.

Generating noise is a simple, cheap, and versatile method of blocking signals or shielding communication from a range of devices. From the disruption of radio broadcasts to the masking of conversations, noise generators use a simple concept to great effect.

Noise is an unpredictable disturbance that causes errors in the transmission of all types of communication. Background chatter at a party, static on a radio, poor handwriting, a patchy cellphone connection, and 'snow' (electronic interference) on a television screen are all examples of noise.

By flooding a frequency, or band of frequencies, with noise, the original communication signal can be drowned in a sea of static. Noise generation has been used to jam torpedo guidance systems and block battlefield communications. During the Cold War the broadcasts of Radio Free Europe and the Voice of America were often jammed by Soviets using a network of radio transmitters that covered the entire Soviet Union. In the 1970s the British government jammed pirate radio stations in an attempt to maintain control of the airwaves.

However, by far the most widespread use of noise generators is as a countermeasure against listening devices. The monitoring of conversations is not an activity limited to the world of spies. Companies and individuals are often bugged by rivals seeking to gain private information, and government agencies often spy on the activities of suspected individuals, illegal or otherwise. While removing potential bugs is the surest way to avoid being overheard sometimes this is not possible, or there are doubts that all the listening devices have been detected. Acoustic noise generators can stop the monitoring of spoken conversations from microphone and tape recorders, transmitting bugs, carrier current transmitters, through-wall devices, laser bounce listening equipment, and infrared transmitters. Because they can protect against such a wide variety of covert devices, and do not require the bugs to be found, acoustic noise generators are versatile and popular security items.

Further Reading

Books

Johnson, William, with Jack Maguire. Who's Stealing your Business?: How to Identify and Prevent Business Espionage. New York, NY: AMACOM, American Management Association, 1998.

Petersen, Julie K., Understanding Surveillance Technologies: Spy Devices, their Origins & Applications. Boca Raton, FL : CRC Press, 2001.