TRANSMISSION LINES 



289 



stations, one at Elkton and one at Baltimore. Additional repeater 

 stations were established accordingly at in-between points — Holly Oak, 

 Abingdon, and Laurel. One of these repeater points, Holly Oak, was 

 established in a local telephone office. No such convenient housing 

 existed at the other two points, and it was necessary to establish new 

 repeater stations. These were small metal structures large enough 

 to house only the repeaters, their power supply, and testing equipment. 

 This apparatus was arranged to be normally non-attended, various 

 switching actions being remotely controlled from the nearest regular 

 repeater station. 



4 8 12 16 20 24 28 32 36 40 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 2 — Line attenuation characteristic of typical repeater section. 



The line attenuation between repeater points is shown in Fig. 2. 

 It may be noted that the attenuation is approximately 50 db for the 

 highest carrier frequency involved. A diagram showing the variations 

 in power level as the carrier waves traverse the complete circuit is 

 shown in Fig. 3. Because of the variation in attenuation over the 



13 20 



UJ 



m 



O 



S-20 



-^0 



O-60 



Fig. 3 — Transmission level diagram. 



frequency range employed it was necessary, of course, to use equalizers 

 at the input of each repeater; i.e., networks having an attenuation 

 variation with frequency approximately the inverse of that of the line 

 circuit. 



