Neiv Television and Radio Services 133 



was essential; and this would not necessarily be the case with 

 television. But there are certain fundamental differences be- 

 tween radio transmission and reception and the transmission 

 of television that alter the problem. 



In order to understand the problems of bringing television 

 to the homes throughout the length and breadth of America, 

 it is important to grasp the difference between transmission of 

 the radio waves used to transmit sound radio today and the 

 high-frequency waves which are used to transmit television. 

 Radio waves at a frequency of from five hundred and fifty 

 to fifteen hundred kilocycles can travel great distances because 

 they are reflected back from the ionosphere, a layer of charged 

 particles which encircles the earth. While the "ground waves" 

 from a radio station might travel in a straight line from the 

 transmitting antenna thirty or forty miles, these "sky waves" 

 which are reflected may shoot out into space two hundred 

 miles or more; strike the ionosphere; and be reflected back to 

 earth several times, traveling halfway around the earth or 

 even farther. 



But the waves at the frequencies used to transmit television 

 are not reflected back to earth. They travel in a straight line, 

 so that they can be sent only as far as one can see from the 

 antenna which is transmitting them. Of course, the higher the 

 antenna the farther the waves can be sent. But even from 

 the highest antenna available today, television reception can- 

 not be depended on farther away than an area fifty miles wide 

 around the transmitting station. We know that the networks 

 of sound-radio stations are hooked up by telephone lines. But 

 telephone cables cannot transmit television in a satisfactory 

 manner. The only type of cable which is satisfactory is a 

 type called "coaxial," and the expense of laying but one co- 

 axial cable across the continent would run into millions of 

 dollars. 



