ADVANCES IN CARRIER TELEGRAPH TRANSMISSION 



191 



Operation Over Carrier Telephone Circuits 

 Where v-f. telegraph operates through the same repeaters as one 

 or more telephone circuits, as in the case of carrier-telephone systems, 

 a new form of variable interference arises due to the changing load 

 conditions introduced by variations in voice volume. Where there 

 are comparatively few telephone channels involved, as in the type C 

 carrier-telephone system for instance, there is very little averaging and 

 the voice peaks determine the repeater load which is effective in 



25 



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12 13 14 15 16 17 18 19 20 21 22 23 24 25 



output LEVEL OF TRANSMITTING REPEATER (ABOVE SWITCHBOARD LEVEL) IN DECIBELS 



Fig. 17 — Voice-frequency telegraph operated over an open-wire carrier-telephone 

 circuit. Effect of associated telephone channels on telegraph distortion, 



causing interference to telegraph. This interference is due in part to 

 changes in net-loss of the circuit resulting from the non-linearity of 

 amplification and in part to intermodulation between the various 

 currents passing through the repeaters simultaneously. Figure 17 

 gives an example of the distortion produced in a telegraph circuit 

 operating over one channel of a 3-channel telephone system when the 

 other two are occupied by two equal-volume talkers. The marked 



