Detectors

Branly Coherer
(Replica)

A detector is a device that converts a high frequency radio signal into a low frequency audio signal that can be heard through headphones or amplified and played through a loudspeaker. The very first detectors were used only to detect the presence of an electromagnetic pulse, since modulation hadn't been developed, and communication was accomplished by transmitting electromagnetic pulses in Morse code. One such detector was the Coherer, used by Marconi in its earliest receivers.

By the early 1900's the coherer had been replaced by various crystal technologies capable of detecting high frequency AM radio signals By the mid-teens, vacuum tube detectors such as the DeForest Audion were also popular. Below are several of the detectors in my collection:

Marconi Magnetic Detectors c. 1904
Known as the "Maggie", it was the standard detector used on ships from 1902 to 1914. Click here for more information.

Cover in place

Cover removed

This is another Maggie I own, which has no cover.

Epochet Ball Coherer
4th qtr 19th century
(German)

The Ball coherer consists of a glass tube enclosing several steel balls. It operates on the "dirty contact" principle discovered by Hughes. An adjustment at the top of the tube provides a way to vary the pressure on the stack, thereby changing the electrical characteristics of the detector.

Lowenstein SE 183-A Triple Detector 1917	Unknown Early Crystal Detector c. 1915	Adams Morgan Crystal Detector Approx. 1916
Lowenstein SE 184-A Galena Detector 1918	Adams Morgan CR 1235 Si/An Detector 1919	Westinghouse DB Dual Detector 1921
Kilborne & Clark Galena Detector Seattle, WA	Krows Electric Co. Galena Detector Seattle, WA	Krows Electric Co. Galena Detector Seattle, WA
A.W. Bowman Galena Detector Sold in 1917 by Sears, Roebuck & Co. as the "Universal Detector Stand."	Unmarked Early Crystal Detector	Electro Galena Detector 1914
Wireless Specialty Perikon Detector	Wireless Specialty Pyron Detector	Marconi Coherer 1895-1905 One of the first devices used by Marconi to detect RF signals. Click here for more information
Early Unidentified Crystal Detector	DeForest Tubular Audion 1916 Click here for more informaton Fleming Valve (British) 1910 The Fleming valve is considered to be the grandfather of all thermionic vacuum tubes. Click here for more information.	DeForest Spherical Audion c. 1914

Thanks to Craig Smith for the following background on the "SE" designation: The Bureau of Steam Engineering came into being July 1,1910--commanded by Rear Admiral Hutch I. Cone. Among their other (more steam related activities) they were responsible for "providing radio stations and equipment and for maintaining them." Prior to 1910 the Navy had used a mostly civilian Wireless Board to advise in procurement of civilian radio apparatus. The Bureau of .S.E. and the Naval Research Lab shared design responsibility and to some extent manufacture of some radio items. Those items designed by the Bureau carried the "SE" prefix. Other items, like the CR1235 detector were designed by outside firms and adopted by the Navy. The "CR" prefix in this case stands for Wireless Specialty Co. Adams-Morgan must have built them under license.

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