Radio Detectors


Branly Coherer

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By the early 1900's the coherer had been replaced by various crystal technologies capable of detecting high frequency AM radio signals  By the mid-teens, vacuum tube detectors such as the DeForest Audion were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

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

Unknown Early Crystal Detector
c. 1915

Adams Morgan
Crystal Detector
Approx. 1916

Lowenstein SE 184-A
Galena Detector

Adams Morgan CR 1235

Westinghouse DB Dual Detector

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

Wireless Specialty Perikon Detector

Wireless Specialty Pyron Detector

Marconi Coherer

One of the first devices used by Marconi to detect RF signals. Click here for more information




Early Unidentified Crystal Detector

DeForest Tubular Audion
here for more informaton


Fleming Valve
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.