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A covert listening device, more commonly known as a bug or a wire, is usually a combination of a miniature radio transmitter with a microphone. The use of bugs, called bugging, or wiretapping is a common technique in surveillance , espionage and police investigations.
a white noise source (used for unvoiced sounds); a signal generator (used for voiced sounds) generating a set of harmonics , with the base frequency controlled by the pitch signal; a switch, controlled by the voiced/unvoiced signal, to select one of these two as a source;
ActiveVFP (also known as AVFP) is a server-side scripting framework designed for Web development to produce dynamic Web pages.Similar to PHP, but using the native Visual Foxpro (VFP) language and database (or other databases like Microsoft SQL and MySQL), ActiveVFP can also be used in Model-View-Controller (MVC) web applications as well as RESTful API.
resistors: the braking resistors of electric trains, used to dissipate electrical power when the catenary is not receptive during braking, can make electromagnetically induced acoustic noise; coils: in magnetic resonance imaging, "coil noise" is that part of total system noise attributed to the receiving coil, due to its non-zero temperature.
Telephone hybrid transformer at the interface of the four-wire long-distance trunk and the two-wire local loop. Z B is the balance termination. NBOC is the network build-out capacitor, which is set to the average shunt capacitance through the telephone central office switch. Red arrows show relative current flow.
The originating end of the call would play the tone into the trunk line when the call ended, and trigger the remote end to end the call. After a short time, the originating end reduced the tone level and continued to send tone as long as it received on hook status from its local equipment.
Different types of noise are generated by different devices and different processes. Thermal noise is unavoidable at non-zero temperature (see fluctuation-dissipation theorem), while other types depend mostly on device type (such as shot noise, [1] [3] which needs a steep potential barrier) or manufacturing quality and semiconductor defects, such as conductance fluctuations, including 1/f noise.
Foxhole radios consisted of a wire aerial, a coil of wire serving as inductor, headphones, and some sort of improvised diode detector to rectify the signal. Detectors consisted of an electrical contact between two different conductors with a semiconducting film of corrosion between them. They were devised from various common objects.