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Loose Couplers

Also known as a "Receiving Transformer", loose couplers were used extensively in receivers built during the "teens". The coupler consists of two coils, a primary and a secondary. The primary coil is stationary and is usually provided with a slider for varying the inductance by single turns. The secondary coil slides in and out of the primary to vary the coupling, and is designed with several switch points in order to change its inductance.

Loose couplers were used as the primary tuning device in early receivers. The primary coil was attached to an antenna and ground (sometimes through a variable condenser.) The secondary was connected to a detector (typically a crystal detector in the early sets.. see detectors for more information.)

 



Simple crystal radio using loose coupler

By the early 20's the loose coupler had lost favor as a tuning element to variometers and variocouplers, 
with their advantage of smaller size and panel mounting. Below are some examples of loose couplers 
in my collection:

 


Murdock Loose Coupler
1913

 


Murdock Loose Coupler
1914
 


Arlington Receiving Transformer
1915




Navy type Loose Coupler
1917


Unidentified Loose Coupler
c.  1916


Adams Morgan #520
1920


Clapp Eastham
Slide Coil Tuner
1912


Unidentified Loose Coupler
c.  1916


Tel-Radion Loose Coupler
c.  1912


William B. Duck
Loose Coupler
1916

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