CROSSTALK AND NOISE FEATURES 



157 



channel per repeater section, at the repeater input. If there were 

 no other noise sources, the repeater section length would necessarily 

 be limited by this effect. Curve B shows the sum of thermal noise 

 and noise due to the vacuum tubes in the repeaters, which is little 

 in excess of thermal noise alone. The other three curves show 

 noises of considerably higher magnitude which require suppression in 

 order to arrive at an economical carrier system. Curve E shows the 

 order of magnitude of noise on carrier circuits due to connecting open- 

 wire pairs directly to non-carrier pairs in the outside cable near the 

 carrier repeater input. The source of the noise is heavy atmospheric 

 static of a magnitude experienced several times during the summer. 



(/)0 

 _|Z 



CQUJ 



2> 

 zo 



■15 



15 20 25 30 35 40 45 



FREQUENCY IN KILOCYCLES PER SECOND 



50 



60 



Fig. 15 — Noise, subsequent to suppression measures, per repeater section at 

 output of repeater whose gain equals line loss. 



A to E — Same sources as in Fig. 14. 



F — Noise from heavy static induced directly into outside cable. 



The other curves show typical magnitudes of noise originating in the 

 existing telegraph and voice frequency telephone plant; this is gen- 

 erated in existing repeater stations and transmitted by the non-carrier 

 pairs to the outside cable where it is induced into the carrier pairs. 

 Curve D represents the situation at a combined telephone and tele- 

 graph repeater station, and Curve C, the situation at a station where 

 there are no telegraph repeaters. 



Figure 15 indicates the results after suppression measures have been 

 applied. As shown, at the top frequency, which controls the carrier 

 repeater section length, these sources of noise have been reduced to be 

 well below thermal plus tube noise. It is also shown that the noise due 



