Tl-.LF.I'UOSl- IR.IXSMISSIDX M.ll \ I i;\'ANCr. 47 



•J. MlCASlRKMKNTS ()!• NolM: 



Tin.- rninmon iiuiIuhI of mi-asurinn noisi- in ;i Iflrplioiu- ciniiil \4 

 ^liown ill tlu- diagram of l-'in- 12. In tliis test an arliluial noisi- 

 curront prodiu'cd by a jifnt-rator of constant povvrr /', c.illrd a "noist- 

 standard" is substituted for the line noise iiirrenl. It ilic two noise 

 currents were exactly alike as regards wave shaiie and tlic relative 

 magnitude of the frequencies involved they would ])roduce the saint- 

 tone in the receiver and their Nolumes could be made e(iual by afl- 

 justnunt of the noise shunt. The power ratio, Pr/Ps, as indicated 



■a ^'— i^X 



Ctrcuit uoder Test 



Me3«urscT)ent.s of Noise 

 Fig. 12 — Diagram Showing Principles of Noise Measurements 



by the shunt, would then give a measure of the line noise in terms 

 of the noise standard. This condition, liowexer. is not met wiili in 

 practise due to differences in wa\e shape of the two noise currents. 

 For this reason noise measurements are made by adjusting the noise 

 shunt until the interfering eflfects of the noise on the line and from 

 the shunt are judged to be the same for which condition the jiower 

 -upplied to the receiving network by the noise standard is not neces- 

 sarily the same as that supplied by the line. The receiving end 

 im[)edances however, arc kept as nearly alike as practicable to pre- 

 vent reflection losses. 



3. Mr.vsirkmf.nts of Lini;-Xi:tw()RK B.\!..\n< ic (21-(iR(iir 

 B.\i,.\N( !•: Ticsr) 



The testing arrangement of Fig. 13 shows the princijile of the 21- 

 circuit balance test referred to in the main body of the paper in 

 connection with telephone repealer and carrier maintenance. In 

 this test the gain of an amplifier calibrated in 'I'U is used to com- 

 pen,s.-ue for the loss through a three winding transformer or output 

 coil of a telephone repeater. If the impedances of the balancing 

 network and line were exactly alike at all frec|uencies, i.e., Z„=Z[.. 

 .ind no other unbalances existed in the circuit none of the power 

 supplied by the amplifier to the input of the three-winding trans- 



