. The Bell System technical journal . k coupling between open-wire circuits and the general typesinto which it is convenient to divide the crosstalk effect. The usualmeasures of crosstalk coupling will also be discussed. Causes and Types of Crosstalk The crosstalk coupling between open-wire pairs is due almost entirelyto the external electric and magnetic fields of the disturbing these fields were in some way annulled there would remain thepossibility of resistance coupling between the pairs because of leakagefrom one circuit to the other by way of the crossarms and insulators,tree
. The Bell System technical journal . k coupling between open-wire circuits and the general typesinto which it is convenient to divide the crosstalk effect. The usualmeasures of crosstalk coupling will also be discussed. Causes and Types of Crosstalk The crosstalk coupling between open-wire pairs is due almost entirelyto the external electric and magnetic fields of the disturbing these fields were in some way annulled there would remain thepossibility of resistance coupling between the pairs because of leakagefrom one circuit to the other by way of the crossarms and insulators,tree branches, etc. This leakage effect is minor in a well-maintainedline. It enters as a factor in the design of open-wire transpositionsonly in so far as the attenuation of the circuits is affected whichindirectly affects the crosstalk. Figure 1 indicates cross-sections of two pairs of wires designated as1-2 and 3-4. If pair 1-2 existed alone and if the two wires weresimilar, a voltage impressed at one end of the circuit would result in. Fig. 1—Magnetic field produced by equal and opposite currents in wires 1 and 2. 22 BELL SYSTEM TECHNICAL JOURNAL equal and opposite currents at any point. These currents wouldproduce a magnetic field as indicated on the figure. If circuit 3-4parallels 1-2 a certain amount of this magnetic flux would threadbetween wires 3 and 4 and induce a voltage in circuit 3-4 which wouldresult in a crosstalk current in this circuit. This induced voltage is,of course, due to the difference between the two magnetic fields setup by the opposite directional currents in wires 1 and 2. Since wires1 and 2 are not very far apart, the resultant field is much weaker thanif transmission over wire 1 with ground return were attempted. It isimportant, therefore, that the wires of a circuit be placed as closetogether as practicable and that these wires be similar in material andgauge in order to keep the currents practically equal and opposite. Equal and opposite charges ac
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