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A Brief History of the Crystal Diode

Cat's whisker

The cat’s whisker

Crystal diode technology began its development in the early 1900s, where wireless receivers utilised a thin wire that made mechanical contact against the face a crystal. The wire had to be manually adjusted to find the ‘hot-spot’ on the crystal for best radio wave detection. This device allowed current to pass in one direction only, and so rectified the received carrier signal to provide a D.C. voltage that could drive headphones.


germanium point contact diode

A cut-away view of a Hughes Germanium Glass Diode (1954)

Within a few years germanium/galena ‘cat-whiskers’ were being used by amateur radio enthusiasts and in early commercial radios. The development of radar systems during WWII then led to a demand for a more reliable high frequency, low-noise detector/mixer – the diode.

Millions of silicon crystal diodes, such as the 1N21, were manufactured in the 1940s for military radar use. Sylvania pioneered the use of germanium for diodes, with the introduction in 1946 of the 1N34 – the first commercial germanium crystal diode.