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Lessons in Wireless Telegraphy

Chapter 27: LESSON TWENTY-FOUR. LOOSE COUPLERS.
By Alfred Powell Morgan
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About This Book

This work presents a compact, lesson-based introduction to the physical principles behind wireless telegraphy, aiming to give operators a clear theoretical grounding. Arranged in discrete lessons, it starts with magnetism, magnetic induction, and basic electrochemical cells, then develops circuit laws and the components and methods for producing, radiating, and detecting electromagnetic signals. Emphasis is on clear explanations, illustrative diagrams, and simple experiments to show how transmitters, receivers, antennas, and tuning interact, while detailed engineering and maintenance procedures are deferred to a companion volume.

LESSON TWENTY-FOUR. LOOSE COUPLERS.

A Loose Coupler or Receiving Transformer is a tuning coil in which the coupling, as well as the inductance, is variable. We have already explained that an ordinary transmitting set throws off two sets of wave trains of slightly different length, one being somewhat weaker than the other.

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FIG. 53. Loose Coupler.

The purpose of the loose coupler is not only to adjust the receiving set to the period of the transmitter in the manner of the tuning coil, but by varying the coupling to attract the apices of the weaker trains of waves to the same apex as the stronger waves and so really create a pure wave out of the other two.

This may be more easily understood from the accompanying illustration which represents diagrammatically a double train of waves and a pure train.

In construction, the loose coupler consists of a primary winding much the same as an ordinary tuning coil provided with a single slider.

A second winding called the secondary, divided into a number of sections and adjustable by means of a multi-pointed switch mounted on one end, slides in and out of the primary.