Intraquad far-end crosstalk in local cables

Based on the quasi-transversal crosstalk theory, the process of origin of far end crosstalk in twisted line systems is explained using a theoretical line model. As far as intraquad far end crosstalk is concerned, formulas making possible numerical calculation from the geometric cable dimensions are derived from this model. It is calculated that the intraquad far end crosstalk is entirely real and proportional to the cable length, the coupling period, and the square of the frequency. It is mainly caused by double near end crosstalk via third lines. The factors determining crosstalk, such as line parameters, operating conditions (closed, open, short) as well as coupling functions between the lines are separately examined. Furthermore, methods are presented for determining these important parameters either by calculation or by measurement. The crosstalk portions of all third lines as calculated on the basis of the theory, are analyzed and show the strong influence of the unsymmetrical lines.