TWELVE-CHANNEL OPEN-WIRE CARRIER SYSTEM 



367 



large amount of information has been accumulated. These tests have 

 shown that the shape of the attenuation-frequency characteristic differs 

 considerably for different ice formations and even if the ice deposit 

 remains the same for a time, the attenuation-frequency characteristic 

 may vary with temperature as in Fig. 2. The two upper curves of the 

 figure were measured at different times during the same storm. There 



1 



Fig. 3 — Ice on wires and insulators near Amarillo, Texas. 



was no apparent change in deposit between the two measurements. 

 This change in shape of the characteristic, of course, makes the 

 regulation problem more difficult. In spite of the extreme severity of 

 ice effects in certain regions, it is expected that satisfactory reliability 

 will be obtained on type J systems by placing the repeaters sufficiently 

 close together. 



Regulation Problem 



In the first type J systems the regulator, actuated by a single pilot 

 frequency in each direction, compensates for the attenuation changes 

 caused by temperature and wet weather. 



The required varieties of attenuation slopes with ice on the wires 

 could not be provided by a simple regulator. Hence provision is to 

 be made in later designs for a regulator with variable slope controlled 

 by two pilot frequencies which is expected to be satisfactory in areas 

 subjected to sleet conditions. The regulating range will also be 

 increased so that a completely automatic control of gain up to about 

 75 db will be available. 



It was found that during periods when ice coated the wires the 



