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A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena ...
A radio direction finder (RDF) is a device for finding the direction, or bearing, to a radio source. The act of measuring the direction is known as radio direction finding or sometimes simply direction finding (DF). Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately ...
A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations. A modern communications receiver, used in two-way radio communication stations to talk with remote locations by shortwave radio. Girl listening to vacuum tube console radio in the 1940s.
Digital multimedia broadcasting (DMB) and DAB-IP are both suitable for mobile radio and TV because they support MPEG 4 AVC and WMV9 respectively as video codecs. However, a DMB video subchannel can easily be added to any DAB transmission, as it was designed to be carried on a DAB subchannel.
The Thing (listening device) The Thing, also known as the Great Seal bug, was one of the first covert listening devices (or "bugs") to use passive techniques to transmit an audio signal. It was concealed inside a gift given by the Soviet Union to W. Averell Harriman, the United States Ambassador to the Soviet Union, on August 4, 1945.
The dynamic cone loudspeaker, invented in 1924, greatly improved audio frequency response over the previous horn speakers, allowing music to be reproduced with good fidelity. [21] AM radio offered the highest sound quality available in a home audio device prior to the introduction of the high-fidelity, long-playing record in the late 1940s.
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. Self-contained electronic covert listening devices came into common use with ...
The term radio receiver is understood in this article to mean any device which is intended to receive a radio signal in order to generate useful information from the signal, most notably a recreation of the so-called baseband signal (such as audio) which modulated the radio signal at the time of transmission in a communications or broadcast system.