174 BELL SYSTEM lECllSICAL JOVRNAL 



is principally a funclion of the load characteristic of the modulator 

 and it shows that for inputs greater than 1 mil, the modulator is 

 overloaded. In practice the overloading of the modulator is pre- 

 vented by increasing the average low frequency line equivalent to an 

 attenuation of 10 T.L'. bv means of a resistance artificial line. This 



Fig. 24 — Tniiismilting Ciriiiit Load Characteristic 



arrangement is desirable in order that the balancing of the low fre- 

 quency hybrid coil may not be complicated when operating over very 

 short physical circuits. 



The curve in Fig. 25 is a single frequency quality characteristic 

 and shows that where the method employed for connecting to the 



AUDIO FREOUENCY IN CYCLES 



tOOO 2M0 3000 IMO lOOC 



Fig. 25 — Single F'reqiieiuy Quality Cliaractcristic 



power line will permit, remarkably true voice transmission may be 

 secured. The \ariation in the e(]ui\alent o\er the range from 100 

 cycles to 5,000 c\-cles is only 51^ T.U., while the variation from 300 

 cycles to 5,000 cycles is only 2 T.U. Reference to Fig. 10 will indi- 

 cate, however, that less satisfactory quality characteristics are ob- 



