Detector (radio)

In electronics, a detector is an older term for an electronic component in a radio receiver that extracts information contained in a modulated radio wave, a demodulator. The term dates from the first three decades of radio (1886-1916). Unlike modern radio stations which transmit sound (an audio signal) on the radio carrier wave, the first radio transmitters transmitted information by wireless telegraphy, using different length pulses of radio waves to spell out text messages in Morse code. So early radio receivers did not have to extract an audio signal (sound) from the incoming radio signal, but only detect the presence or absence of the radio signal, to produce clicks in the receiver's earphones representing the Morse code symbols. The device that did this was called a detector. A variety of different detector devices, such as the coherer, electrolytic detector, and magnetic detector, were used during the wireless telegraphy era.

After sound (amplitude modulation, AM) transmission began around 1920, the term evolved to mean a demodulator, a nonlinear rectifier (usually a crystal diode or a vacuum tube) which extracted the audio signal from the radio frequency carrier wave. This is its current meaning, although modern detectors usually consist of semiconductor diodes, transistors, or integrated circuits.

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