Detectors 090
Detectors 090 : Particle Detectors: (4.3) Cat's-Whisker Detector: (3) Types: From the earliest wireless telegraphy days of radio, well into the age of commercial AM broadcasting, unamplified radio receivers were powered only by the radio energy they picked up through their antennas. The crystal radio was the most widely used of these. Manufactured and homemade by the millions, it helped introduce radio to the public, contributing to the development of radio from an experimental hobby to an entertainment medium around 1920. After about 1920, receivers using crystal detectors were largely superseded by the first amplifying receivers, which used vacuum tubes. These did not require the fussy adjustments that crystals required, were more sensitive, and also were powerful enough to drive loudspeakers. Nevertheless, the expense of the early vacuum tubes and the batteries needed to run them meant that the crystal detector remained in commercial and military use for almost a decade more. However, by the late 1920s, radios using crystal detectors were relegated to use by hobbyists and youth groups and have been used by them as educational devices to the present day. The point-contact semiconductor detector was subsequently resurrected around World War II because of the military requirement for microwave radardetectors. Vacuum-tube detectors do not work at microwave frequencies. The small area of the point contact minimized minority carrier storage and capacitance, making these diodes fast enough to function at radar frequencies. Silicon and germanium point-contact diodes were developed. Wartime research on p-n junctions in crystals paved the way for the invention of the point-contact transistor in 1947. The germanium diodes that became widely available after the war proved to be as sensitive as galena and did not require any adjustment, so they replaced cat's-whisker detectors in the few crystal radios still being made, largely putting an end to the manufacture of this antique radio component. Although cat's-whisker detectors are obsolete, modern point-contact silicon detectors are still commercially produced. Thus, the point-contact method used to make these first semiconductor diodes 100 years ago is still being used today
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