288 BELL SYSTEM TECHNICAL JOURNAL 



200 to 1500 ft. One of the interesting problems in connection with 

 their design is the provision of means for allowing variation in length 

 with temperature. Ordinary expansion joints introduce difficulties 

 with electrical contacts and impedance irregularities. To avoid these 

 the lines are made 10 per cent longer than otherwise necessary and they 

 follow a sinuous course which permits the necessary bending. Sharp 

 turns are not permissible because experiments have shown that they 

 cause reflection disturbances. The measured loss in 1000 ft. of line 

 at 20,000 kilocycles is 2 db. 



Receiving Station 



The radio problems encountered in the layout of the receiving sta- 

 tion, in general, include most of those already mentioned in connection 

 with the transmitting station, but their solution in some instances is 

 quite different. In addition there are requirements imposed by sources 

 of radio noise both within the station itself, and in the surrounding 

 area which is beyond the control of the station. 



The number of antennas is determined, of course, by the frequency 

 assignments of the distant transmitting station. Where two assign- 

 ments are within 100 kilocycles it is possible to use the same antenna for 

 both, but thus far, this has not been done at Netcong. 



The size of the antennas is not limited appreciably by the length of 

 transmission lines because other factors make it necessary to separate 

 them rather widely. On this account and also because the receiving 

 apparatus and its power plant are small, comparatively inexpensive 

 units, it is economical to place the receivers in small buildings centrally 

 located with respect to the group of antennas for one channel. In this 

 case the lengths of transmission lines are not controlling factors and the 

 dimensions of antennas are governed primarily by the considerations 

 previously outlined when describing the individual antenna. The 

 small height of the antenna permits them to be placed in the line of 

 reception of other antennas spaced ten wave-lengths or more away and 

 of widely different frequencies such as those of one channel. Antennas 

 adjusted for the same order of frequency are separated more than this. 

 On the other hand, to avoid adverse reactions no two are placed adja- 

 cent and end-to-end as at the transmitting station. The end-to-end 

 separation at Netcong is in the order of four wave-lengths. The areas 

 surrounding antennas are cleared of trees and kept free of all overhead 

 wires or conducting structures to avoid reflection effects which disturb 

 the directional characteristic of the antenna systems. 



The locations of antennas are also influenced materially by the neces- 

 sity of avoiding interference from the ignition systems of internal 



