356 



BELL SYSTEM TECHNICAL JOURNAL 



20 50 100 500 1000 5000 10,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 3 — Attenuation characteristics of 8-inch spaced open-wire pairs when inserted 

 between 600-ohm resistances. 



that all coincide at 1,000 cycles; thus a direct comparison of the differ- 

 ence in shape of the attenuation frequency characteristics may readily 

 be observed. 



Figure 4 shows resistance and reactance components of 165-mil 

 and 128-mil 8-inch spaced open-wire lines. Note that, except at low 

 frequencies, the impedances of the various open-wire lines are quite 

 uniform throughout the frequency range and do not depart greatly 

 from 600 ohms. For this reason and in consideration that the majority 

 of telephone apparatus is designed for 600-ohm impedance, all units of 

 this new program system, except the carrier line filters, have been 

 designed to have an impedance of 600 ohms. In order to reduce 

 reflection losses, particularly in the carrier range, the line filters have 

 been designed to have an impedance on the line side somewhat lower 

 than 600 ohms although the drop or office side impedance is 600 ohms. 



Attenuation Equalizers 

 To furnish the necessary attenuation corrections for the three 

 different gauges of lines, four adjustable attenuation correcting net- 

 works have been provided. One attenuation equalizer provides atten- 

 uation correction for high frequencies only and is common for all 

 gauges. The three other equalizers provide low-frequency attenuation 

 correction designed specifically for the particular gauge of circuit the 



