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Lessons in Wireless Telegraphy

Chapter 29: LESSON TWENTY-SIX. VARIABLE CONDENSERS.
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-SIX. VARIABLE CONDENSERS.

The point of sharpest resonance does not always happen to come on a turn of the tuner where it can be reached by the slider. The variable condenser makes it possible to adjust the circuit to the exact point of resonance.

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FIG 56. Rotary Variable Condenser.

Variable condensers are of two general types, the Sliding Plate and the Rotary Variable. The rotary variable is the most convenient and easy to manipulate. It consists of a number of fixed semi-circular metal plates between which swings a set of smaller movable semicircular plates. The fixed plates form one half of the condenser and the movable plates the other. In this way the capacity of the condenser is very closely adjustable. The movable plates are provided with a pointer moving over a graduated scale so that the comparative amount of capacity in the circuit is indicated.

The sliding plate type of condenser consists of a number of rectangular fixed plates between which slide a set of movable plates.

The dielectric between the plates of a variable condenser is air. There are no losses of energy due to hysteresis in a condenser having an air dielectric. Rotary condensers employing silk or some such material are not to be recommended.