Detectors 088
Detectors 088 : Particle Detectors: (4.3) Cat's-Whisker Detector: (3) Types: The goal of researchers was to find junctions that were not as sensitive to vibration and unreliable as galena and pyrite. Some of these other junctions, particularly carborundum, were stable enough that they used a more permanent spring-loaded contact rather than a cat's whisker. For this reason, carborundum detectors were preferred in large commercial wireless stations and military and shipboard stations that were subject to vibration from waves and gunnery exercises. Another quality desired was the ability to withstand high currents without damage, because in wireless stations, the fragile detector junction could be "burned out" by atmospheric electric charge from the antenna or high radio frequency current leaking into the receiver from the powerful spark-gap transmitter during transmissions. Carborundum detectors, which used large-area contacts, were also particularly robust in this regard. To increase sensitivity, some of these junctions such as silicon carbide were "biased" by connecting a battery and potentiometer across them to provide a small constant forward voltage across the junction. The oxide layers that form on many ordinary metal surfaces have semiconducting properties, and detectors for crystal radios have been improvised from a variety of everyday objects such as rusty needles and corroded pennies. The foxhole radio was a crystal radio receiver improvised by soldiers during World War II without access to conventional sets. It used a razor blade and a safety pin or lead pencil to form a demodulating junction. Much patience was required to find an active detecting site on the blade. Stray rectifying junctions between metal parts of radio transmitter installations are still a source for interference, because they can radiate harmonics of the transmitter frequency
No records Found