490 



BELL SYSTEM TECHNICAL JOURNAL 



merits were fulfilled. (For measurements and performance of the 

 complete line circuit see footnote 15.) 



1,000 

 Frequency (cycles per second) 



moo 20.000 



Fig. 19 — Time-of-phase-transmlssion characteristics of television circuit before and 

 after distortion correction. 



4.5. Equalization of Variable Attenuation in Carrier Telephone Circuits 

 An open-wire circuit, such as used in a carrier system, is exposed to 

 various weather conditions along the line and consequently experiences 

 considerable changes in its transmission characteristics, primarily its 

 attenuation. For satisfactory operation of carrier circuits the total 

 circuit attenuation must ordinarily be kept reasonably constant. 



One practical and advantageous method of maintaining a constant 

 circuit attenuation which takes into account weather changes as well 

 as length differences in the successive repeater sections is the following. 

 Each repeater section is built out and equalized with terminal networks 

 such that at all times the total attenuation has the same uniform value 

 in the desired frequency range. This is done by means of two kinds 

 of networks, a variable artificial line and a base attenuation equalizer. 

 The variable artificial line builds out any given section to correspond 

 to what is effectively under wet weather conditions the maximum 

 line section used, and the base attenuation equalizer makes this total 

 attenuation of the section uniform in the frequency range under 

 consideration. Then the total attenuation of any line section, arti- 

 ficial line, and attenuation equalizer has the same constant value over 

 the frequency range and will thus be in proper adjustment with a 

 repeater having a fixed gain. 



