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BELL SYSTEM TECHNICAL JOURNAL 



loading, and a special loading arrangement having a slightly lower cut- 

 off was, therefore, designed for this cable. 



Equalization 



Requirements. The requirements for the lines were stated earlier. 

 In order to meet these overall requirements it was necessary to apply 

 special forms of distortion-correcting networks. 



Weather Changes. The above requirements applied, of course, to 



10D 1D00 



FREQUENCY - CYCLES PER SECOND 



10,000 20,000 



Fig. 3 — Computed phase delay (/3/co) of television circuit with and without equalizers 



all of the various weather conditions to which an open-wire circuit is 

 subject. Due to the changes in the leakage conductance occurring 

 at the insulators, the attenuation of an open-wire circuit varies with 

 changing weather conditions. This change is particularly important at 

 the higher frequencies. At 20,000 cycles, for example, the attenuation 

 of a 165-mil open-wire pair may vary as much as 40 per cent for a 

 change from dry weather to extra wet weather. For the circuit 

 between Washington and New York this represents a possible at- 

 tenuation change of about 10 T U, or a change of 10 to 1 in the magni- 

 tude of the received power. At 1000 cycles, the effect of wet weather 

 is comparatively small, so that the net effect of the weather variations 

 is to change the requirements for the attenuation equalizers. The 

 phase shift introduced by an open-wire pair likewise varies to some 

 extent with changes of weather, although the percentage variation 

 is much smaller than in the case of the attenuation. In view of 



