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BELL SYSTEM TECHNICAL JOURNAL 



measurements of the cross-talk are made in the side circuits, the 

 cross-talk bein^ exj^ressed in milhonths of the current into a trans- 

 former connected to the phantom circuit and of such ratio as to make 

 the impechuice al its injjut equal to that of the side circuit. As a 

 result of the imioroxements previoush- mentioned, the average cross- 

 talk in the coils used for the H-44-2o loading is now about 20 millionths. 

 This corresponds to an attenuation f)f about 95 TU. 



To assist in \'isualizing the real achievement which this minute 

 \alue of phantom-to-side cross-talk represents. Table XIV gives 

 information regarding the cross-talk of different elementary types of 

 unbalance in H-44-25 loading coils: 



TABLE XIV 



Cross-talk Due to Unbalance in H-44-25 Loading Coils 



Type of Unbalance 



Amount of Cross-talk 



1 ohm resistance 



1 micro-henry inductance 



1 turn of winding 



1 micro-microfarad capacitance 



400 milhonths ( 68 TU) 

 2.5 " (112 TU) 



280 " ( 71 TU) 



0.94 " (121 TU) 



These values apply at 1,000 cycles. 



In the loading coils designed for H-174-63 loading, the cross-talk 

 per unit of electromagnetic unbalance tends to be smaller and the 

 cross-talk per unit of electrostatic unbalance larger, in rough propor- 

 tion to the differences in line impedance betw^een the H-44-25 and 

 H-174-63 circuits. 



Side-to-side cross-talk is uniformly lower than phantom-to-side 

 cross-talk, as would be expected from the less intimate coupling 

 between circuits. Accordingly, the special adjustments which are 

 made are primarily for the purpose of reducing phantom-to-side 

 cross-talk. 



In the loading coils intended for H-44-25 circuits the special cross- 

 talk adjustments are applied for minimizing "far-end" cross-talk or 

 for minimizing "near-end" cross-talk, according as the coils are re- 

 quired for four-wire or two-wire repeatered circuits, respectively. 

 The term "far-end" cross-talk applies to cross-talk heard at the 

 distant end of the disturbed circuit, and correspondingly the term 

 "near-end" cross-talk applies to the cross-talk heard at the end of 

 the distm-bed circuit near the talker. 



