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Lessons in Wireless Telegraphy

Chapter 22: LESSON NINETEEN. THE KEY.
By Alfred Powell Morgan
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Engineering & Technology

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 NINETEEN. THE KEY.

Some means of controlling the currents flowing through the transmitter in order to divide them into periods corresponding to the dots and dashes of the Morse Code is necessary.

This is supplied by a hand operated switch, called a key. A key used for wireless purposes must be much larger and heavier than an ordinary key employed for line work in order to carry the more powerful currents.

In spite of the size and weight of a wireless key, if it is properly balanced, it may be handled with perfect control and ease.

The contact points of a wireless key are necessarily large and heavy. Special alloys found to be the most suitable for the purpose are usually employed. A large condenser having a mica dielectric is very often connected across the contacts to reduce the sparkling.

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FIG. 42. Wireless Key.

In very large stations where extremely heavy currents must be handled, the key controls a large switch operating in oil. Every time the key is pressed the switch closes and when the key is released, opens. The currents of the transmitter are "made" and broken by the switch without passing through the key.