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

摘要

METHOD AND APPARATUS FOR MEASURING THE SURFACE TRANSFER IMPEDANCE OF A PIECE OF SHIELDED CABLE A method for measuring surface transfer impedance of shielded cable within a frequency range below about 1 GHz is implemented with a single test fixture. The test fixture provides a conductive cylindrical chamber which opens for installation of a sample of shielded cable. The ends of the chamber are blocked by ferrite toroids to prevent radiation of high frequency electromagnetic energy. One end of the cylindrical chamber may be externally short-circuited to the cable shielding for low frequency measurements. current source connects between the sample shielding and the conductive chamber boundary at the other end of the chamber. Current flow at low frequencies is limited to the region between the current source and the short circuit. Current flow at high frequency is limited to the region between the toroids. The cable shielding and the fixture body beyond the toroids are short-circuited for high-frequency tests and open-circuited for low frequency tests. The induced voltage in the cable is measured through feed-throughs provided in the test fixture. The current source uses an isolation transformer to avoid ground loops in the low-frequency range.