File:Crystal radio circuit with bias and buzzer.svg
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[edit]DescriptionCrystal radio circuit with bias and buzzer.svg |
English: A crystal radio receiver circuit with detector bias battery and testing buzzer. This type receiver circuit was used with cat's whisker detectors during the wireless telegraphy era prior to the 1920s. Many of the crystals used in early cat's whisker detectors, particularly carborundum (silicon carbide), had large band gaps (forward voltage drops). These weren't very efficient rectifiers in crystal radios, because the low voltage signal from the antenna had to overcome the device's forward voltage drop, and so was insufficient to drive the device far into its conduction region, so it had a large AC resistance. To make the detector D1 more sensitive, an adjustable bias voltage equal to the forward voltage drop is applied by battery B1 and potentiometer R1 across the detector. For silicon carbide about 1 V was used. R1 was adjusted until the radio station sounded loudest in the earphone. The bias moved the DC operating point to the most sensitive "knee" of the detector's IV curve The cat's whisker detector D1 consisted of a fine wire touching the surface of a piece of crystal. The metal-crystal contact functioned as a primitive PN junction, allowing current to flow in only one direction. Only certain sites on the crystal surface functioned as rectifying junctions, so an active site had to be found by trial and error before each use. The operator dragged the wire across the crystal surface until the detector began functioning. The battery-powered buzzer circuit (B2, BZ, S1) generated a test signal to determine if the detector was functioning. Switch S1 was closed and the electromagnet-operated buzzer BZ was turned on while the detector was adjusted. The sparks at the buzzer's contacts acted as a weak radio transmitter, and its signal was applied to the receiver's ground wire. So when the right spot on the detector was found, the buzz could be heard in the earphones. Then the buzzer was turned off. |
Date | |
Source | Own work |
Author | Chetvorno |
SVG development InfoField | This diagram was created with Inkscape, or with something else. This diagram uses translateable embedded text. |
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[edit]Public domainPublic domainfalsefalse |
I, the copyright holder of this work, release this work into the public domain. This applies worldwide. In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law. |
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Date/Time | Thumbnail | Dimensions | User | Comment | |
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current | 04:12, 9 May 2017 | 672 × 672 (43 KB) | Chetvorno (talk | contribs) | Replaced with "plain SVG" version that passes validation | |
02:19, 28 January 2016 | 672 × 672 (56 KB) | Chetvorno (talk | contribs) | Increased line width and tweaked location of components | ||
06:17, 29 May 2010 | 686 × 688 (58 KB) | Chetvorno (talk | contribs) | {{Information |Description=A Wikipedia:crystal radio circuit with detector bias battery and testing buzzer. This type circuit was used with Wikipedia:cat's whisker detectors during the wireless telegraphy era prior to the 1920s. Many of the cry |
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