![]() More sophisticated envelope detectors include the grid-leak detector, the plate detector, the infinite-impedance detector, transistor equivalents of them and precision rectifiers using operational amplifiers.Ī product detector is a type of demodulator used for AM and SSB signals, where the original carrier signal is removed by multiplying the received signal with a signal at the carrier frequency (or near to it). The limited frequency response of the headset eliminates the RF component, making the low pass filter unnecessary. A later version using a crystal diode is still used in crystal radio sets today. If the resistor and capacitor are correctly chosen, the output of this circuit will be a nearly identical voltage-shifted version of the original signal.Īn early form of envelope detector was the crystal detector, which was used in the crystal set radio receiver. The simplest form of envelope detector is the diode detector that consists of a diode connected between the input and output of the circuit, with a resistor and capacitor in parallel from the output of the circuit to the ground to form a low pass filter. One major technique is known as envelope detection. Amplitude modulation detectors Envelope detector A simple envelope detector A simple crystal radio with no tuned circuit can be used to listen to strong AM broadcast signals In microwave and millimeter wave technology the terms detector and crystal detector refer to waveguide or coaxial transmission line components, used for power or SWR measurement, that typically incorporate point contact diodes or surface barrier Schottky diodes.Ī coherer detector, useful only for Morse code signals. The mixer is called the first detector, while the demodulator that extracts the audio signal from the intermediate frequency is called the second detector. In a superheterodyne receiver the term is also sometimes used to refer to the mixer, the tube or transistor which converts the incoming radio frequency signal to the intermediate frequency. This is its current meaning, although modern detectors usually consist of semiconductor diodes, transistors, or integrated circuits. ![]() A variety of different detector devices, such as the coherer, electrolytic detector, magnetic detector and the crystal detector, were used during the wireless telegraphy era until superseded by vacuum tube technology.Īfter the invention of amplitude modulation (AM) enabled the development of AM radiotelephony, the transmission of sound (audio), during World War 1, the term evolved to mean a demodulator, (usually a vacuum tube) which extracted the audio signal from the radio frequency carrier wave. The device that performed this function in the receiver circuit was called a detector. Therefore, early radio receivers did not have to demodulate the radio signal, but just distinguish between the presence or absence of a radio signal, to reproduce the Morse code "dots" and "dashes". ![]() The transmitter was switched on and off to produce long or short periods of radio waves, spelling out text messages in Morse code. ![]() Unlike modern radio stations which transmit sound (an audio signal) on an uninterrupted carrier wave, early radio stations transmitted information by radiotelegraphy. The term dates from the first three decades of radio (1888-1918). In radio, a detector is a device or circuit that extracts information from a modulated radio frequency current or voltage.
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