Detector (disambiguation): Difference between revisions

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A detector is a device capable of registering a specific substance or physical phenomenon.

Detector may also refer to:

Detector (radio), a device that recovers information from a modulated wave
Detector (film), a 2000 Norwegian film
USS Detector, two United States Navy ships
- USS Detector (AMc-75), was a coastal minesweeper launched 29 May 1941
- USS Detector (AM-429), was a minesweeper launched 5 December 1952

This disambiguation page lists articles associated with the title Detector.
If an internal link led you here, you may wish to change the link to point directly to the intended article.

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+{{wiktionary|detector}}
-:''This article is about radio electronics. For the general use of the term ''detector,'' see '''[[Sensor]]'''. For optical detectors, see '''[[Photodetector]]'''.''
+A '''[[detector]]''' is a device capable of registering a specific substance or physical phenomenon.
+'''Detector''' may also refer to:
-In a radio receiver, a '''detector''' is a [[electrical network|circuit]] or device that recovers the [[Signal (information theory)|signal]] of interest from the modulated wave.
+* [[Detector (radio)]], a device that recovers information from a modulated wave
-In the early days of [[radio]], all transmissions were in [[Morse Code]], and so it was really only necessary to have some means of detecting the presence (or absence) of a radio signal, not necessarily making it audible. For example, the detector used by [[Heinrich Hertz]] for his pioneering 1888 radio transmission experiments consisted of nothing more than a circle of metal with a tiny gap cut in it. When his transmitter was operating, a tiny spark would jump the gap, which could be observed with a microscope.
+* [[Detector (film)|''Detector'' (film)]], a 2000 Norwegian film
+* [[USS Detector|USS ''Detector'']], two United States Navy ships
+** {{USS|Detector|AMc-75}}, was a [[coastal minesweeper]] launched 29 May 1941
+** {{USS|Detector|AM-429}}, was a minesweeper launched 5 December 1952
+{{disambiguation}}
-The first practical detector (ie one that could work any appreciable distance from the transmitter) was the [[Coherer|Branley Coherer]], invented by Dr [[Edouard Branley]] of France. Branley had originally been experimenting with some intesting electrical properties of glass tubes full of metal filings. Initially the filings would not conduct electricity, but once a critical voltage was reached, he found they would abruptly "cohere" and the electrical resistance would drop to a very low value. After that, they would continue to conduct even with very low voltages applied; that is the device would become permanently "switched on". However, lightly tapping the tube would restore the high-resistance condition.
-At the same time Branley had been doing other, unrelated experiments with a high-voltage induction coil, and he noticed that whenever he produced an electrical discharge (ie a miniature lightning bolt) the filings would cohere as though the high voltage had been applied, even though there was no obvious physical connection between the two electrical systems. Other researchers soon realized that Hertz's radio waves were actually responsible and [[Marconi]] used a Branley Coherer as a detector in his first experiments. His version was simply a copy of Branley's device attached to an [[electric bell]]. Whenever a radio signal was being transmitted the filings would cohere, allowing current to pass through the bell and make it ring. By mounting the coherer on the bell itself, the vibration of the ringing would immediately kill the coherence, but it would be continuously be restarted as long as the radio signal was present. Hence stopping and starting the radio signal (with a Morse Code key for example) would make the electric bell ring in sympathy with it.
-However, this system was only useable for [[on-off keying]] modes and more sensitive systems were sought. It had long been known that a telephone earpiece could serve as an extremely sensitive indicator of weak electrical signals, but they could not respond to the high-frequency [[alternating current]]s of radio transmission. Various methods were used make these signals audible, including devices, like the [[electrolytic detector]] and the [[hot wire barretter]]  Other early 20th century detector devices included the [[magnetic detector]] and the [[Audion]] tube, which was the forerunner of modern [[vacuum tube]]s.
-Basically, what was needed was some device that would allow only the positive or negative half-cycles of the radio signal through, converting them to pulses of DC which the telephone earpiece could respond to.  Thomas Edison had accidentally discovered and patented such a device some years before, based on one of his light bulbs, but he could never think of any practical use for it. A British Physicist, Sir [[Ambrose Fleming]] produced an improved version in 1904, which he called his Electron Valve (since it allowed current to flow in only direction) and is now known as a [[diode]] valve or tube. The same principle is still in wide use today, and the function of extracting intelligence from radio signals is still referred to as detection, althought the term [[demodulation]] is the preferred technical term.
-Although Fleming's original devices were very useful for precision laboratory work, for general communications they weren't particularly efficient, compared to competing devices. Around 1906 researchers discovered that certain metallic minerals such as [[Galena]] also could be used to yield a demodulation action, at a considerably lower cost and with no power consumption and this became known as the [[crystal detector]]. In WWII, an improved version based on [[germanium]] became known as the germanium diode, initially for use in Radar receivers, and later developed into the transistor and eventually all other solid-state devices.
-Although the demodulators used in FM receivers and most television sets work on quite different principles to those used for AM demodulation, the term "Detector" is still widely applied to these also.
-[[Category:Detectors| ]]
-[[Category:Radio electronics]]
-[[Category:Measuring instruments]]