TRANSOCEANIC TELEPHONE SERVICE 275 



the application of high-voltage direct current, the entire system starts 

 up and shuts down in the proper sequence in response to the manipula- 

 tion of a master control switch. 



Direct current at 10,000 volts is supplied to the anodes of the power 

 amplifier tubes by a transformer and rectifier using six standard two- 

 electrode thermionic tubes. The rectified current is filtered separately 

 for each stage of the amplifier. This is necessary to prevent distortion 

 by interstage modulation caused by the common impedance of the 

 rectifier. Effects of this nature become important as the requirements 

 placed on unwanted modulation products become more stringent. 



Transmitting Antennas 



The antennas at Lawrenceville all have comparatively sharp direc- 

 tional properties. Such antennas are readily realized when dealing 

 with radio waves of very short wave-lengths. Although the funda- 

 mental principles involved in producing these directional effects have 

 been known for many years, economic limitations effectively prevented 

 their application to transmitting antennas for long wave-lengths. 

 These limitations are altered immensely in the case of antennas for 

 short wavelengths and, when the useful propagation properties of short 

 waves became known, great stimulus was given to the development of 

 antennas for directional sending and receiving. The same type of 

 antenna can be used, of course, for both purposes but, since the objec- 

 tives when sending and receiving are somewhat different, the tendency 

 has been to develop arrangements adapted to each case. 



Directional transmission is a very large subject and will only be 

 touched upon suflficiently to describe in a very general way the anten- 

 nas at Lawrenceville. There are many possible arrangements and 

 combinations and the engineers must choose from these the ones most 

 suitable for their purpose. In general all of the schemes depend upon 

 producing interference patterns which increase the signal intensity in 

 the chosen direction and reduce It to comparatively small values in 

 other directions. 



One of the methods of obtaining a sharply directive characteristic is 

 to arrange a large number of radiating elements in a vertical plane 

 array, spacing them at suitable distances and interconnecting them in 

 such a manner that the currents in all the radiating members are in 

 phase. A simple way of accomplishing this result and the one which 

 is now being employed at Lawrenceville depends upon the manner in 

 which standing waves are formed on conductors. It is generally known 

 that current nodes and current maxima will recur along a straight 

 conductor whose length is an exact multiple of one half the wave-length 



