64 BELL SYSTEM TECHNICAL JOURNAL 



end and, furthermore, these losses change by varying amounts with 

 temperature and weather conditions. It is the function of the regu- 

 lating equipment to provide the needed adjustment and equalization 

 of levels over the wide range of line conditions. 



The theory of the operation of the regulating system is shown in a 

 simplified manner in Fig. 11. The line circuit is connected at the end 

 of each repeater section to a line equalizer, which is in turn connected 

 to an artificial line unit designed to be continuously variable. The 

 slope of the line equalizer loss characteristic is the reverse of the line 

 slope and is as great as may be found in practice on any ordinary 

 length of line section except under conditions of severe ice or frost. 

 The artificial line slopes in the same direction as the line circuit itself. 

 In lining up a system the artificial line is adjusted so that when 

 added to the real line the slope of the combination neutralizes that of 

 the equalizer leaving the overall transmission very nearly uniform for 

 all frequencies in the range. Then as the loss and slope of the real 

 line change, the artificial line is made to change in the reverse direction 

 leaving the overall transmission still uniform. The action of this 

 artificial line is under the control of the pilot current, referred to 

 before, and the design of the equipment is such that in maintaining 

 the pilot at the proper level the other channels are also properly 

 adjusted. 



In practice, the regulating unit must take care of a wide variety of 

 wire sizes, wire spacings and insulator types. It has been found, 

 however, that the change in slope for a given change in attenuation 

 at some reference frequency is very nearly the same for all combinations 

 of the above during ordinary weather conditions. As a result a single 

 unit can be made to serve all cases. 



Where conservative repeater spacings are employed there is a large 

 amount of regulating range available to take care of sleet or frost 

 formations on the wires. For the particular use illustrated in Fig. 11 

 the total range is about twice that required for ordinary wet weather. 

 For shorter sections the available range would be still greater. 



Some details of the regulating equipment are shown on Fig. 12. 

 The pilot frequency is selected from the other frequencies on the line 

 by a narrow band filter bridged across the output of the amplifier. 

 This filter has a high impedance so that the bridging loss is small and 

 does not interfere with regulation at succeeding stations. 



A copper-oxide varistor is used to convert the selected pilot frequency 

 into direct current which in turn actuates two Weston Sensitrol 

 relays connected in series. The relays are equipped with meter scales 

 on which a needle attached to the armature serves as a pointer. One 

 of these relays controls the action of the regulator, the other functions 



