WIRELESS TELEPHONE 



6327 



WIRELESS TELEPHONE 



makes and breaks the circuit, or, if a trans- 

 former is used, the alternations produce a cor- 

 responding effect, for at the end of each alter- 

 nation the current dies down to zero. At each 

 interruption or reversal of the primary current 



I/IP- vfA. Jlf* JlT- JVv Jfc v/^V^xf^V/^ 



FIGURES A AND B 



the electric waves that are being sent out die 

 down to zero. This may happen with an ordi- 

 nary spark coil a hundred or more times a sec- 

 ond; there would be just that many interrup- 

 tions to the sound of the voice if a person were 

 to attempt to use a spark coil for wireless 

 telephony. 



The electric waves sent out by a spark coil 

 or transformer may be represented by a broken 

 wave line, as in a in the illustration. The waves 

 of the speaking arc are uniform and uninter- 

 rupted, as in 6. While the electric oscillations 

 produce vibrations in the receiver that are so 

 rapid that the ear cannot detect them, the 

 sound of the voice modifies these oscillations 

 so that they produce slower vibrations in the 

 receiver. In the illustration d represents the 



c v/wwwwvw^ 



FIGURES C, D, E 



sound waves and c the electric waves as modi- 

 fied by the sound waves. If the interrupted 

 waves of the spark coil were used to transmit 

 speech, the sound would also be interrupted, as 

 shown in 6. 



The Transmitter. The carbon granule or mi- 

 crophone transmitter (see TKU.PIH>M-:) i> 

 in nearly all systems of wireless telephony; 

 this is the same form of transmitter as that 

 i in tin- \vm telephone. The oscillations 

 produced by the speaking arc flow through the 

 carbon granules as the battery current flows 

 through the carbon granules of the wire i 

 phone transmitter. When a person speaks into 

 the transmitter the diaphragm which presses 

 against the carbon granules is set in vibration. 

 As the diaphragm vibrates, it varies the prcs- 

 -u re on the carbon granules. When the pro- 

 is increased a stronger charge can i 

 through the carbon granules; when the pressure 



is reduced the oscillations are made weaker. 

 The transmitter, therefore, acts in the same 

 way toward the electric oscillations as the wire 

 telephone transmitter acts toward the battery 

 current which flows through it. As the oscilla- 

 tions are made alternately stronger and weaker 

 by the sound waves acting upon the diaphragm, 

 the electric waves going out from the aerial 

 are alternately stronger and weaker, and the 

 changes in the electric waves correspond per- 

 fectly to the sound waves. This stream of elec- 

 tric waves changing with the sound of the voice 

 transmits the message as does the alternating 

 current in the wire telephone. 



It is probable that the electric oscillations 

 set up in the earth by the transmitter aid in 



TRANSMITTING SYSTEM 

 (1 ) Telephone trans- ( 5 ) Reactance 

 (6) Condenser 



mitter 



(2) At-rial 



(3) Arc 



(4) Dynamo 



(7) Copper plate in 

 ground 



producing the effect upon the receiver, both in 

 wireless telegraphy and wireless telephony. The 

 grounding of the wires at both stations is nec- 

 essary for long-distance transmission, and the 

 f condition of the earth between the two sta- 

 tions, whether moist or dry, has a marked ef- 

 fect on the transmission. 



The power required for the wireless tele- 

 phone is much greater than for the wire tele- 

 phone. The reason is that with wireless trans- 

 mission the electric energy goes out in all 

 directions and much of it is lost. Because so 

 much ^rn ater pov, : red a specially con- 



structed transmitter must be used, one that 

 will not be injured by the strong currents tint 

 surge through it. 



he sake of simplicity we have assumed 

 that the oscillations from the arc flow through 



