256 BELL SYSTEM TECHNICAL JOURNAL 



' In very loni; lines having llie newer grades of loading, the line losses 

 are still sutficient to cause serious attenuation distortion effects if 

 allowed to go uncorrected. The improved types of repeaters now 

 used on long loaded circuits provide somewhat higher gains at the 

 upper speech frequencies, thereby obtaining approximately, a flat 

 frequency characteristic over a wider frequency range. In repeaters 

 need in conjunction with the H-44-25 loading, losses are introduced 

 at the lower speech frequencies by auxiliaries to the repeater circuit, 

 for the purpose of flattening the frequency characteristic at low 

 frequencies. An indication of the improvement obtainable in the 

 above ways is given by a dot- dash curve in Fig. 11, which illustrates 

 the attenuation-frequency characteristic of a 500-mile H-44-S cir- 

 cuit having the best types of repeaters nr)w commercially available. 



In \'iew of the difficulties brought into repeatered circuits by the 

 use of loading, the question comes up: "Why not use more repeaters 

 and do without the lotiding?" In the case of long cable circuits the 

 answer to this question is that the coil loading substantially improves 

 the attenuation and substantially reduces the frequency distortion 

 at a cost which is much lower than the cost of the additional repeaters 

 and distortion corrective networks which would be required to gi\e 

 the same grade of transmission without using loading. 



Long Repeatered Open Wire Lines. In the case of the long open 

 wire lines, the present day answer to the foregoing question is un- 

 favorable to the use of loading. The use of improved types of repeaters 

 now makes it possible to secure better transmission results in long 

 repeatered circuits without loading, than can be secured in loaded 

 repeatered lines. In this connection it should be noted that in the 

 case of non-loaded open wire lines the distributed inductance is 

 sufficiently large to keep the attenuation-frequency distortion low. 

 Also the velocity of transmission is very high relative to that of a coil 

 loaded line and there is no cut-off effect except that pnxluced by the 

 filters and other apparatus in the repeater sets. 



These general transmission considerations are resulting in (he 

 removal of coil loading from high grade open wire lines. This dis- 

 mantling work is being accelerated in order to adapt the open wire 

 plant for a much more extensive application of carrier telephone and 

 carrier telegraph systems. 



The present expectations are that in the future new applications 

 of open wire loading will generally be limited to isolated cases of 

 short lines where carrier telephone or telegraph systems are not 

 contemplated and where the maintenance and operating conditions 

 are unfavorable to the use of telephone repeaters. 



