METHOD AND APPARATUS FOR MEASURING THE SURFACE TRANSFER IMPEDANCE OF A PIECE OF SHIELDED CABLE

摘要

METHOD AND APPARATUS FOR MEASURING THE SURFACETRANSFER IMPEDANCE OF A PIECE OF SHIELDED CABLEABSTRACTA method for measuring surface transferimpedance of shielded cable within a frequency rangebelow about 1 GHz is implemented with a single testfixture. The test fixture provides a conductivecylindrical chamber which opens for installation of asample of shielded cable. The ends of the chamber areblocked by ferrite toroids to prevent radiation of highfrequency electromagnetic energy. One end of thecylindrical chamber may be externally short-circuited tothe cable shielding for low frequency measurements.current source connects between the sample shielding andthe conductive chamber boundary at the other end of thechamber. Current flow at low frequencies is limited tothe region between the current source and the shortcircuit. Current flow at high frequency is limited tothe region between the toroids. The cable shielding andthe fixture body beyond the toroids are short-circuitedfor high-frequency tests and open-circuited for lowfrequency tests. The induced voltage in the cable ismeasured through feed-throughs provided in the testfixture. The current source uses an isolationtransformer to avoid ground loops in the low-frequencyrange.