Chapter 5. Near End Crosstalk (NEXT)In one-cable operation, errors can be caused by NEXT between cable pairs in opposite directions of transmission. Physically separating the different groups of pairs as much as possible is preferred. Refer to Figure 8. Shortening the repeater spacings will reduce the level differential and the sensitivity to NEXT. One single T-1 system in a cable has only itself with which to interfere (transmit signal with respect to receive signal). Twenty systems in a cable makes many more cases for NEXT. Not only does one single system have itself for interference, but nineteen other systems are also producing NEXT. If a particular cable use is expected to grow over time to its maximum capacity, then the correct safety margin must be calculated into the design. This cannot be corrected later.
Figure 8
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