WIRELESS TELEPHOISrY. 
By N. H. Slaughtek, D. S. M., 
Engineering Department, Western Electric Co., Neic York, N. Y., (formerly) 
Lieutenant Colonel, Signal Corps, United States Army. 
[With 6 plates.] 
FUNDAMENTAL REQUIREMENTS. 
The development of wireless telephony dates back almost as far as 
the original conception of the use of electromagnetic waves for wire- 
less telegraphy. The practical utilization of this method of com- 
munication is, however, a matter of comparatively recent date as con- 
trasted with the much longer period during which wireless telegraphy 
has been a practical accomplishment. This delay in the successful 
utilization of wireless telephony is due to certain differences in the 
fundamental requirements as comj^ared with those for the telegraph. 
These differences and the manner in which the particular difficulties 
incident to the successful accomplishment of wireless telephony have 
been overcome will be explained in detail in succeeding paragraphs. 
Broadly speaking, the principal difference between wireless tele- 
phony and wireless telegraphy lies in the form of the signal which 
has to be transmitted, telegraph signals being obviously far simpler 
in the wave-form of the signal current than are telephone signals. 
The fundamental requirement is in either case that the form of the 
received signal shall faithfully reproduce the form of the trans- 
mitted signal, whether due to the opening and closing of a telegraph 
key or the vibrations of a telephone transmitter diaphragm. 
The essential units required in a complete wireless telephone system 
may be grouped into the transmitting and the receiving elements. 
The receiving elements, being in no respect different from those re- 
quired in wireless telegraphy, will not be described at this point. 
The transmitting elements differ, however, in many respects and 
comprise the following essential units : 
A radio frequency generator. 
A modulator for controlling the radio frequency current. 
An antenna for radiating the electromagnetic waves pro- 
duced by the r^dio frequency current. 
* Presented at a joint meeting of the electrical section and the Philadelphia section, 
American Institute of Electrical Engineers, held Thursday, Oct. 30, 1919. Reprinted by 
permission from the Journal of the Franklin Institute, January, 1920. 
177 
