Early History
During World War II, lookouts aboard surfaced German submarines used handheld crystal-video radar receivers called ATHOS to detect pulses emitted by search radars on Allied warships and aircraft This type of receiver consisted of a tuning coil and capacitor to select the approximate radio frequency to be received; a crystal diode, usually of silicon, that acted as a one-way gate, or rectifier, and produced an audible sound; and a simple amplifier that broadcast the “detected” sounds over a headset or loudspeaker. After the war, this same technology was adopted and applied in the direction-finding systems of American warships and airplanes because of its simplicity, small size, and “wideopen” frequency-detection characteristics.
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