OPEN-WIRE CROSSTALK 219 



connection with carrier telephone, or, in some cases, program trans- 

 mission circuits. At these frequencies near-end crosstalk limits must 

 be set so as to limit the induced noise from the carrier telegraph. 



When the type unbalance crosstalk limits are finally determined, 

 the transposition designer must attempt to meet the requirements for 

 all circuit combinations and all the transposition sections. It may be 

 that the requirements can not be met and consideration must be given 

 to modifications in the nature of the transmission systems. A vast 

 amount of such preliminary transposition design work has been 

 necessary in order to evolve the present transposition systems and 

 transmission systems. 



Such studies led to the development of non-phantomed circuits 

 with 8-inch spacing since they indicated that multi-channel long-haul 

 carrier operation on all pairs on a line was, in general, impracticable 

 from the crosstalk standpoint with 12-inch phantomed pairs. 



It may be noted that there are also difficulties in the crosstalk 

 problem when 12-inch phantomed pairs are used for voice-frequency 

 repeatered circuits. These circuits have a crosstalk advantage over 

 carrier circuits in that the frequency is lower but they have an off- 

 setting disadvantage in that they use the same frequency range in 

 both directions. This makes the near-end crosstalk directly audible 

 to the subscriber. As previously discussed the near-end crosstalk is 

 inherently greater than the far-end crosstalk and, for this reason, 

 practicable designs of multi-channel carrier systems do not allow near- 

 end crosstalk to pass to the subscriber, the path being blocked by 

 one-way amplifiers. While it takes fewer transpositions to control 

 the type unbalance effects with voice-frequency transposition designs, 

 for a given length of parallel the difficulties with crosstalk due to 

 irregularities are about as great as with designs for multi-channel 

 carrier operation. 



The simple example of Fig. 29 illustrates the reasons for the diffi- 

 culties with near-end crosstalk with the voice-frequency designs for 

 12-inch spaced pairs. It also illustrates the method of deducing the 

 permissible crosstalk per repeater section as discussed above. 



This figure indicates two paralleling repeatered circuits, each having 

 six repeater sections of 10 db loss and five repeaters of 10 db gain. 

 The net loss of each circuit is, therefore, 10 db. The near-end crosstalk 

 values in the six sections are indicated by Wi to «6- The crosstalk 

 coupling at A due to m is just equal to W2 since there is no net loss or 

 gain in either circuit between A and B. There is also no net loss or 

 gain between A and C, A and D, A and E or A and F. The total 

 crosstalk coupling at A is, therefore, the vector sum of the six values 



