256 



OUR PHYSICAL WORLD 



The simple wireless receiving equipment consists of appliances 

 for intercepting these trains of high-frequency ether waves and con- 

 verting them into electrical vibrations which can bemade to produce 

 mechanical vibrations of audible frequency in a telephone receiver. 



f 



wave- 



o 

 wave- 



FIG. 114. A train of damped waves 



A simple wireless receiving outfit may consist 

 of (Fig. 115), (a) the antenna for receiving the 

 ether waves, (d) a detector for converting these 

 waves into electrical impulses of audio frequency, 

 (r) a telephone receiver for converting the elec- 

 trical impulses into mechanical vibrations, and 

 (g) a ground connection. 



The receiving antenna is not necessarily so 

 large as the sending antenna, and may consist 

 of a single wire suspended between high points 

 above surrounding buildings or trees and about 

 1,000 feet in length. Much simpler antennas 

 have been found to be very successful. Wires 

 suspended in an attic are sometimes employed, 

 and even small loops of wire within a room are 

 very efficient with sensitive receiving equipment. 

 Even bed springs and fire escapes give fair results 

 when not many miles from the sending station. 

 The detector is the distinctive part of the 

 radio-receiving circuit. There are a great num- 

 ber of types of detectors. They all consist of 

 an arrangement whereby the electrical oscillations are rectified 

 or made to flow principally in one direction with the result 

 that a pulsating current of audio frequency flows through 



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 C/ 



FIG. 115. 

 Diagram of a 

 simple receiving 

 set. 



