EMI (electromagnetic interference) test procedures specify thatlong cables should be bundled at their center in some circumstances. Theauthor investigates the effect of cable bundling using analytical modelsand measurements. He examines how cable bundle parameters such as lengthand `tightness' can affect the repeatability of the measurement. Simplemodels of a bundled cable suggest that relatively small changes in thegeometry of the bundle can significantly affect the common-mode cablecurrent. Parameters such as length, tightness, location and the numberof turns determine the impedance of the bundle. As the impedance of thecable bundle changes, the resonant frequency of the system shifts. Thiscan result in large changes at the very frequencies where EMI problemsare most likely to occur. It is also shown that lossy cables or cableswith a lossy common-mode termination are less likely to be sensitive tominor changes in cable bundle parameters. The resonant peaks in a lossysystem are smaller and cover a wider band of frequencies. Small shiftsin the resonant frequency do not have as much of an impact on thecurrents induced at any one frequency
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