ENCYCLOPEDIA OF Espionage, Intelligence, and Security Volume ...

Audio Amplifiersduring the final days of the Persian Gulf War in February1991; the volcanic eruption of Mount Pinatubo in thePhilippines in June of that year; a sulfuric-acid spill inRichmond, California, in 1993; the reentry of a nuclearpoweredRussian spacecraft over Chile in 1996; and theHanford wildfire in Richland, Washington, in 2000.Though ARAC and NARAC might seem to be virtuallyidentical, the former is an agency of DOE, while the lattersupports both DOE, the Department of Defense, and othergovernmental organizations. Nor are its DOE responsibilitiesconfined to the consequence-management mission ofARAC, though this is certainly a primary activity for NARAC.NARAC also supports other federal, state, and even localagencies in accordance with the Federal Radiological EmergencyResponse Plan and the Federal Response Plan.❚ FURTHER READING:BOOKS:Cassaro, Edward, and Linda Lomonaco. Operators Guide:Atmospheric Release Advisory Capability (ARAC) SiteFacility. Springfield, VA: Department of Energy, 1979.Orphan, R. C. A Study of Applying the Atmospheric ReleaseAdvisory Capability to Nuclear Power Plants.Springfield, VA: Department of Energy, 1978.ELECTRONIC:National Atmospheric Release Advisory Center. (January 14, 2003).SEE ALSOChernobyl Nuclear Power Plant Accident, Detection andMonitoringDOE (United States Department of Energy)Lawrence Livermore National Laboratory (LLNL)Nuclear Detection DevicesAtmospheric Sampling Programs.SEE Environmental Measurements Laboratory.Atomic Bomb.SEE Nuclear Weapons.❚ LARRY GILMANAudio AmplifiersAny electronic device that increases the power of anelectrical signal whose vibrations are confined to theEncyclopedia of Espionage, Intelligence, and Securityaudio frequency range—the range that can be perceivedby the human ear—is an audio amplifier. All devices thattransmit, record, or otherwise electronically process voicesignals employ audio amplifiers. Voice-recognition or voicesynthesissystems, communications or eavesdropping devices,hearing aids, entertainment systems, talking toys,are examples of devices containing audio amplifiers.The need for amplification. Acoustic or sound waves arelongitudinal pressure waves (i.e., waves that cause moleculesto oscillate along the wave’s line of travel rather thanacross it) in air, water, or any other medium. A sound issaid to be in the audio frequency range if it is not too highor low in frequency to be heard by the human ear. Audiosound waves may be converted by microphones intoelectrical signals for analysis, transmission, or recording.Electrical signals can also be converted by speakers intoaudible sound waves. Microphones and speakers are bothtransducers, that is, devices that convert energy from oneform (e.g., electrical) into another (e.g., acoustic) or viceversa. Audio amplifiers are required with both microphonesand speakers.Input amplification. Amplification of the signal produced bya microphone—often termed preamplification—is necessarybecause the electrical signal that can be deriveddirectly from sound waves impinging on a microphone isweak (i.e., on the order of .01 V or less; for eavesdroppingapplications, much less). Input signals of such low amplitudemust be amplified before they can be processed ineither analog or digital circuits.In analog circuits—circuits that process smoothlyvaryingelectrical quantities—there is a always a certainamount of random electrical activity or ”noise.“ This noiseis mixed with any information signal processed by thecircuit, corrupting it. Amplifying a weak input, such as thatfrom a microphone, before it mingles with circuit noisemakes the noise problem manageable. Furthermore, allanalog circuits that lack amplification (passive filters, transmissionlines, etc.) experience signal loss; that is, theydissipate energy. A weak signal fed into a circuit that doesnot contain amplification will, therefore, quickly disappear,making amplification necessary in most analog circuits.Finally, amplification provides electronic isolationbetween the signal being amplified and the result of theamplification process; among other gains, this simplifiesthe circuit-design process.If an audio signal is to be processed using digitalcircuitry (as is often the case today), a digital signal (i.e.,on-off, high-low signal that can represent signal magnitudessymbolically) must be derived from the analoginput. This conversion is performed by a device termed ananalog-to-digital converter. For reasons ultimately derivingfrom the atomic properties of semiconductors, a typicalanalog-to-digital converter requires an analog inputsignal with an amplitude variation on the order of several69