Lessons in Wireless Telegraphy

Chapter 32: LESSON TWENTY-NINE. POTENTIOMETER

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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-NINE. POTENTIOMETER

The potentiometer is an instrument for carefully regulating the voltage of the battery supplying a detector of the electrolytic or carborundum types with current.

It is necessary to bring the potential of the battery to a certain critical point where it is just insufficient to "break down" the detector, that is, overcome the resistance which it offers to the oscillatory currents. In construction, the potentiometer usually consists of a small rod wound with German silver wire and provided with an adjustable contact. Graphite resistance rods are merely a cheap method of making a potentiometer and are to be avoided as entirely unsatisfactory for the purpose.

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FIG. 59. Potentiometer.