STUDIES IN RADIO BROADCAST TRANSMISSION 



149 



we must devise tests which will disclose changes, of whatever kind, 

 in the relations between the various component frequencies of the 

 transmitted band and furnish interpretable permanent records. In 



ATLANTIC OCEAN 



Fig. 3 — Outline map showing locations of transmitting station and receiving test 



stations 



fact in the studies described herein a considerable portion of the job 

 was to devise or perfect suitable methods of attack. 



Single, Double, and Triple Frequency Tests 



The variable factors in radio transmission which may be directly 

 controlled are located at the transmitter and receiver. We have as 

 yet no tangible means of controlling the transmitting medium, but it 

 can be studied indirectly through the characteristics of the received 

 signals. Obviously, it is desirable in the interest of simplicity to 

 stabilize the apparatus variables to the extent that they may be 

 idealized in considering observed results. Furthermore, at both the 

 transmitter and receiver, it is desirable to make the antenna arrange- 

 ments of the simplest form. For our work the normal antenna arrange- 

 ment at station 2XB was used perforce since any important changes 

 would have constituted a major operation. It is far from a simple 

 arrangement, as shown in Fig. 4 which is an outline elevation and plan 

 of the antenna and building at 463 West Street, New York City. For- 

 tunately there are no buildings considerably higher than the antenna 

 within a distance of several wave lengths. 



At the receiving test stations both loop and vertical antenna were 

 used: but in most of the experiments a simple vertical antenna was 

 employed. It was constructed of brass tubing, 30 feet long, and 

 guyed in a vertical position. A galvanized iron pipe 12 feet long 

 was driven in the earth for a ground connection. The vertical re- 

 ceiving antenna projected through the roof of the test station building 



