TRANSOCEANIC TELEPHONE SERVICE 281 



spect to wave-lengths It is possible without objectionable interference, 

 to place the antennas end-to-end and thus use supporting towers in 

 common. Due to the wide difference in wave-length between adjacent 

 antennas and their right-angle position with respect to the line of 

 transmission, their proximity has no appreciable effect different from 

 that of the towers. The proper selection of tower spacing in respect 

 to wave-lengths makes it possible to erect a uniform supporting struc- 

 ture. This has the advantage of flexibility and will permit future 

 alterations of either the location or size of a given antenna. At present, 

 each antenna occupies the space between three towers. 



In order to avoid undue loss In the transmission lines the radio trans- 

 mitters are grouped In two buildings. The buildings each contain two 

 transmitters and are identical In layout, in so far as the radio equipment 

 is concerned. Building No. 1 has additional space for the central wire 

 terminating and testing equipment. This apparatus is contained In an 

 electrically screened room which effectively prevents high-frequency 

 fields from interfering with the proper functioning of the apparatus. 



Receiving System 



Short-wave reception is characterized by less difficulty with static 

 than that encountered with long waves. On the other hand it suffers 

 interference from sources such as the ignition systems of passing air- 

 planes and automobiles, which ordinarily do not disturb long-wave 

 systems. Frequently the Incoming radio waves suffer wide and rapid 

 swings in Intensity and there are variations in the apparent direction 

 of arrival. On account of the extremely high frequencies the ap- 

 paratus and antenna structures are very different from those for the 

 long waves; otherwise the general schemes of reception are similar, 

 directional effects and double detection methods being employed for 

 both. 



The radio wave is collected by means of a directional antenna array 

 whose prime function is to improve the ratio between the desired signal 

 and unwanted noise or other Interference. This It does in two ways: 

 viz., (1) by increasing the total signal energy delivered to the receiver 

 and (2) by discriminating against waves whose directions of arrival 

 differ from the chosen one. Increasing the total energy collected from 

 the incoming message wave permits the detection of correspondingly 

 weaker signals because there is an apparently irreducible minimum of 

 noise inherent to the input circuits of the first vacuum tube in the 

 receiver '" and this noise establishes a lower limit below which signals 

 cannot be received satisfactorily. Since, under many conditions, the 

 ^ J. B. Johnson, Physical Rev., July 1928. 



