wireless coherer
Date: 1895-1905
Inventory Number: DW0096
Classification: Coherer
Dimensions:43 × 27.3 × 13.3 cm (16 15/16 × 10 3/4 × 5 1/4 in.)
DescriptionInstrument is a wireless coherer, used for detecting radio signals during the era of wireless telegraphy. It was invented in 1891 by French scientist Edouard Branley and was originally designed for detecting far off flashes of light. The instrument was adapted in 1895 by Stepanowitch Popoff, and used for detecting wireless waves. It became an important radio technology.
The instrument consists of three components mounted an upright wooden board attached to a wooden base. The first component is mounted on the base, and consists of a wooden panel with four brass binding posts and a brass bracket. Coiled cloth-covered wires connect to the posts. Attached to this is an upright piece with a pair of electrical coils mounted on a brass bracket to the upright. Each of these two components has a removeable wooden box cover, held in place with peg and hook closures.
The upright part of the device contains two components: electrodes spaced closely together with a tube of metal filings in the space between them (the metal filings are missing from this device). One component consists of a wooden block with a pair of electrical coils and 4 brass connection posts with electrical leads. The other component consists of a wooden block with a pair of electrical coils and two brass connection posts connected to a bell and ringer assembly.
It was a key enabling technology for radio, and was the first device used to detect radio signals in practical spark gap transmitter wireless telegraphy. Its operation is based upon the large resistance offered to the passage of electric current by loose metal filings being decreased under the influence of radio frequency alternating current. The coherer became the basis for radio reception around 1900, and remained in widespread use for about ten years.
There are two basic kinds of coherers, the original metal filings type, called the Branley coherer, and a later imperfect junction type.