Sensitivity of Crosstalk in Twisted-Pair Circuits to Line Twist

The prediction of crosstalk induced in an unbalanced twisted pair by an adjacent transmission line is investigated. The induced voltage at one end of the twisted pair is shown, experimentally, to be extremely sensitive to twist for low-impedance loads and relatively insensitive to twist for high-impedance loads. Ex- perimental results are given which show that a slight rotation of one end of the twisted pair ( no more than 1800) can cause a change of as much as 35 dB in the induced voltage. The consequence of these results is that, in a practical situation, one would therefore not be able to predict this crosstalk for low-impedance loads with any con- sistency. A simple model explaining these results is given.