Image from page 551 of "The Bell System technical journal" (1922)
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-16 -14 -12 -10 -8 -6 -4 -2 R.M.S. NOISE-TO-CARRIER RATIO ON LINE IN DECIBELS - Fig. 20—Distortion vs. noise characteristics of frequency-shift arrangements at60 w.p.m. (23 d.p.s.).
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-24 -22 -20 ) -18 -16 -14 -12 -10 -8 -6 -4 -2 R.M.S. NOISE-TO-CARRIER RATIO ON LINE IN DECIBELS Fig. 21—Distortion vs. noise characteristics of various arrangements at 120w.p.m. (46 d.p.s.). 520 CARRIER TELEGRAPH METHODS 521 sistance noise, the noise was introduced into the line through a symmetricalthree-way pad, as previously mentioned. The marking carrier level at oneinput of the noise pad was kept at a constant value. The level of the noisecurrent entering the other input of the noise pad was adjustable, and itsr.m.s. value was measured with a thermocouple, permitting the computationof the r.m.s. noise-to-carrier ratio at the output of the three-way pad, sincethe loss through the pad was the same for both signal and noise. This ratiowas used for abscissae in Figs. 18 to 21, inclusive, and the ordinates representdistortion for various arrangements. These cur\^es are useful in comparingthe relative noise sensitivities of the different arrangements, because the samenoise source was
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