This article is about radio electronics. For other types of detector, see sensor. A detector is a device that recovers information of interest contained in a modulated wave. The term dates from the early days of radio when all transmissions were in Morse Code, and it was only necessary to "Detect" the presence (or absence) of a radio wave using a device such as a coherer; not necessarily making it audible. Not to be confused with censure, censer, or censor. ...
The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ...
For the musical use of modulation, see modulation (music). ...
1922 Chart of the Morse Code Letters and Numerals Morse code is a method for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a message. ...
The coherer was the first device used to detect radio signals in wireless telegraphy. ...
Amplitude modulation detectors
Envelope detector One major technique is known as envelope detection. The simplest form of envelope detector is the diode detector. A diode detector consists of a diode connected between the input and output in a circuit, with a resistor and capacitor in parallel from the output of the circuit to the ground. If the resistor and capacitor are correctly chosen, the output of this circuit will approximate a voltage-shifted version of the original signal. An envelope detector is a device which is used to demodulate AM signals. ...
This elegant example of a modern set was created by VE6AB The crystal radio receiver (also known as a crystal set) is a passive radio receiver consisting of a variable LC circuit tuned circuit, a diode detector, and audio transducer. ...
Closeup of the image below, showing the square shaped semiconductor crystal various semiconductor diodes, below a bridge rectifier Structure of a vacuum tube diode In electronics, a diode is a two-terminal component, almost always one that has electrical properties which vary depending on the direction of flow of charge...
Microwave (crystal) detectors
Product detector A product detector is a type of demodulator used for AM and SSB signals. Rather than converting the envelope of the signal into the decoded waveform like an envelope detector, the product detector takes the product of the modulated signal and a local oscillator, hence the name. This can be accomplished by heterodyning. The received signal is mixed, in some type of nonlinear device, with a signal from the local oscillator, to produce an intermediate frequency, referred to as the beat frequency, from which the modulating signal is detected and recovered. A product detector is a type of demodulator used for AM and SSB signals. ...
A demodulator is an electronic circuit used to recover the information content from the carrier wave of a signal. ...
Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ...
Single-sideband modulation (SSB) is a refinement of the technique of amplitude modulation designed to be more efficient in its use of electrical power and bandwidth. ...
The Superheterodyne receiver (or to give it its full name, The Supersonic Heterodyne Receiver – usually these days shortened to superhet) was invented by Edwin Armstrong in 1918. ...
In telecommunications, to heterodyne is to generate new frequencies by mixing two or more signals in a nonlinear device such as a vacuum tube, transistor, or diode mixer. ...
An intermediate frequency (IF) is a frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception. ...
In telecommunications, modulation is the process of varying a periodic waveform, i. ...
FM and PM detectors Because FM and PM signals have constant amplitude they are incompatible with AM detectors. However an AM radio may detect the sound of an FM broadcast by the phenomenon of Slope Detection which occurs when the radio is tuned slightly above or below the nominal broadcast frequency. Frequency variation on one sloping side of the radio tuning curve gives the amplified signal a corresponding local amplitude variation, to which the AM detector is sensitive. Slope Detection gives inferior distortion and noise rejection compared to the following dedicated FM detectors that are normally used.
Phase detector A phase detector is a nonlinear device whose output represents the phase difference between the two oscillating input signals. It has two inputs and one output: a reference signal is applied to one input. The phase or frequency modulated signal is applied to the other and the output is a signal that is proportional to the difference between the two inputs. This article or section does not cite any references or sources. ...
In phase demodulation the information is contained in the amount and rate of phase shift in the carrier wave. This article or section does not adequately cite its references or sources. ...
The Foster-Seeley discriminator The Foster-Seeley discriminator[1][2] is a widely used FM detector. The detector consists of a special center-tapped transformer feeding two diodes in a full wave DC rectifier circuit. When the input transformer is tuned to the signal frequency, the output of the discriminator is zero. When there is no deviation of the carrier, both halves of the center tapped transformer are balanced. As the FM signal swings in frequency above and below the carrier frequency, the balance between the two halves of the center-tapped secondary are destroyed and there is an output voltage proportional to the frequency deviation. The Foster-Seeley discriminator is an FM detector circuit that works on the same principle as most commonly used FM detectors, which is through variations in frequency. ...
For other uses, see Transformer (disambiguation). ...
A rectifier is an electrical device that converts alternating current to rectified direct current, a process known as rectification. ...
Ratio detector The ratio detector[3][4][5][6]is a variant of the Foster-Seeley discriminator, but one diode conducts in an opposite direction. The output in this case is taken between the sum of the diode voltages and the center tap. The output across the diodes is connected to a large value capacitor, which eliminates AM noise in the ratio detector output. While distinct from the Foster-Seeley discriminator, the ratio detector will similarly not respond to AM signals, however the output is only 50% of the output of a discriminator for the same input signal. Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ...
Quadrature detector Quadrature detectors use a high-reactance capacitor to produce two signals with a 90 degree phase difference. The phase-shifted signal is then applied to an LC-tuned resonant at the carrier frequency. If the frequency changes the phase will also vary and so will the output voltage. It has been suggested that Electric reactance be merged into this article or section. ...
See Capacitor (component) for a discussion of specific types. ...
The phase difference between two signals of the same frequency can be thought of as a delay or advance in the zero crossing of one signal with respect to another. ...
This can also be accomplished by combining the signal and a square wave at the carrier frequency in an XOR gate. The square wave is thus phase shifted 90 degrees with respect to the input carrier modulation. The time interval between the zero crossing of the square wave and the FM signal will depend on the instantaneous frequency, which makes the gate output a pulse whose width depends on the time interval. In essence, the quadrature detector converts an FM signal to a PWM (pulse width modulation) signal. The original audio signal is recovered by passing the PWM resultant through a low-pass filter. A square wave is a kind of basic waveform. ...
This article is about XOR in the sense of an electronic logic gate (e. ...
Pulse-width modulation of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. ...
A low-pass filter is a filter that passes low frequencies but attenuates (or reduces) frequencies higher than the cutoff frequency. ...
Phase-locked loop detector The phase-locked loop detector requires no frequency-selective LC network to accomplish demodulation. In this system, a voltage controlled oscillator (VCO) is phase locked by a feedback loop into following the deviation of the incoming FM signal. The low frequency error voltage that forces the VCO to track is the demodulated output. A phase-lock, or phase-locked, loop (PLL) is an electronic control system that generates a signal that is locked to the phase of an input or reference signal. ...
A voltage-controlled oscillator or VCO is an electronic circuit that uses amplification, feedback and a resonant circuit to generate a repeating voltage waveform. ...
Circle map showing mode-locked regions or Arnold tongues in black. ...
In cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. ...
Level detector One form of level detector is a comparator circuit that compares one inputs with a preset level and provides a DC output indicating when the input signal exceeds this threshold. In electronics, a comparator is a device which compares two voltages or currents and switches its output to indicate which is larger. ...
Input3 is the term denoting either an entrance or changes which are inserted into a system and which activate/modify a process. ...
Other forms of level detector rectify the input signal and give a DC output proportional the peak or RMS level of the input signal. Rectification has the following technical meanings. ...
For quantum-mechanical amplitude, see probability amplitude. ...
RMS may refer to any of the following: Railway Mail Service, US mail transportation service until the mid-20th century Royal Mail Ship or Steamer, ship prefix for vessels that carry mail under contract to the British Royal Mail Royal Melbourne Show Royal Meteorological Society Royal Society of Miniature Painters...
Footnotes - ^ U.S. patent 2,121,103 (inventor: Stuart William Seeley); issued 21 June 1938.
- ^ D.E. Foster and S.W. Seeley, "Automatic tuning, simplified circuits, and design practice," Proceedings of the Institute of Radio Engineers, vol. 25, no. 3, part 1, pages 289-313 (March 1937).
- ^ See: U.S. patent 2,497,840 (inventor: Stuart William Seeley); issued: 14 February 1950.
- ^ See also: U.S. patent 2,561,089 (inventor: Earl I. Anderson); issued: 17 July 1951.
- ^ Report L.B.-645: "Ratio detectors for FM receivers" (15 September 1945) issued by the Radio Corporation of America, RCA Laboratories Industry Service Division, 711 Fifth Avenue, N.Y., N.Y. Reprinted in Radio, pages 18-20 (October 1945).
- ^ Stuart W. Seeley and Jack Avins, "The ratio detector," RCA Review, vol. 8, no. 2, pages 201-236 (June 1947).
See also The coherer was the first device used to detect radio signals in wireless telegraphy. ...
The Hot wire barretter was a demodulating detector invented in 1902 by Reginald Fessenden that found limited use in early radio receivers. ...
The electrolytic detector or the bare-point electrolytic detector as it was also called, was a type of wet demodulator used in early radio receivers. ...
A, Antenna Wire; E, Ground-plate; B B . ...
Cat Whisker Detector A crystal detector in commercial form from the 1960s Cat’s whisker refers to a thin wire that lightly touches a semiconducting crystal to make an imperfect contact-junction detector in a crystal radio. ...
External links Ratio Detector with schematics: http://www.r-type.org/static/add059.htm |
Feeds |
Contact