A TWELVE-CHANNEL CARRIER TELEPHONE SYSTEM 



133 



insulators. It arises from the potential gradient through the ice 

 deposit in combination with the high dielectric loss characteristic of 

 the ice or snow coating. Figure 7 gives examples of the attenuation 



0.8 



0.6 



D 0.4 



0.2 



25 50 75 100 125 



FREQUENCY KILOCYCLES PER SECOND 



150 



Fig. 7 — Attenuation frequency characteristics of open wire lines. 



frequency characteristics of open-wire lines, including certain measure- 

 ments with ice coating. The exact increase in attenuation due to 

 snow and ice naturally depends on the thickness and other character- 

 istics of the coating. Even very thin coatings of ice on the wires 

 tend to raise the attenuation at 140 kc from the normal wet weather 

 figure of about 0.28 db to about 1 db a mile, i.e., an increase of three or 

 four to one. Extremes up to 5 db per mile have been measured for 

 short lengths of line with ice nearly two inches in diameter. Such 

 heavy ice obviously approaches the mechanical breakdown conditions 

 for the line. 



Where ice and sleet occur the repeater spacings may be reduced to 

 about fifty miles or less. The repeaters now being provided for the 

 type J systems have gains of approximately 45 db. Repeaters are 

 under development which are expected to raise the maximum available 

 gain to something like 75 db. The normal dry or wet weather opera- 

 tion of such repeaters would be limited to gains of perhaps 10 to 25 

 db depending upon the amounts of cable included. The problem of 

 obtaining automatic gain control over the extra wide range required 

 by the high sleet attenuations is a difficult one. 



