The principles underlying radio communication Volume 40 - Softcover

Inhaltsangabe

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 Excerpt: ...absorbed by an antenna of the condenser type depends on its capacity, and to form an antenna of large capacity two metal plates would have to be so large as to be very expensive and cumbersome. Instead of using two parallel metal plates, it would be possible, to form a condenser consisting of one metal plate suspended over and parallel to the ground, providing the surface of the ground is appreciably conducting. Such an antenna is shown in Fig. 163. The plate P is supported above the earth and insulated from it, except for the connection through the wire W, called the "lead-in wire," or "lead-in." The plate and the conducting surface of the earth form the two plates of a condenser, the air between them furnishing the dielectric. The apparatus used for receiving is introduced into the lead-in, between the plate and the ground. When radio waves reach an antenna they set up an alternating emf. between the wires and the ground. When an alternating emf. is introduced into the wire, charging currents flow into and out of P and the earth, the dielectric being strained first in one direction and then in the other. As has been explained in the previous chapter, these strains are equivalent to displacement currents of electricity through the dielectric, which serves to complete the circuit. A region in which the dielectric is undergoing alternating strains is the starting point of electric waves. The larger the plate and the higher it is raised from the earth, the greater the amount of space in which this strained condition exists, and the more powerful the waves which are radiated. However, in order to construct with a given amount of metal an antenna having the greatest possible capacity, the metal should not be used in the form of a single plat...

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