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THE TWO CURRENT-PROBE METHOD OF MEASURING CONDUCTED RADIO-FREQUENCY INTERFERENCE
NAVAL CIVIL ENGINEERING LAB PORT HUENEME CA
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A new approach to the problem of measuring conducted interference is described. A brief discussion is presented on the limitations and uncertainties of the presently accepted method using Line-Impedance-Stabilization Networks LISN. These limitations stem from the fact that no information is obtained concerning the impedance values of the circuit being measured during a noise measurement. The new method described provides a means of overcoming the limitations of the present method completely by the use of commercially available current-probes in an impedance- and noise-measurement system. A method of determining the impedance values of the circuit was worked out which requires the use of two current-probes. Either the noise source impedance or the load impedance or both may be determined by this method. Two separate measurements and calculations are required, however one to determine the magnitude of the impedance, and the other to determine the phase angle. An evaluation of the device is presented, as well as numerous examples of noise measurements showing the correlation between measured and predicted results. The precision of the impedance-measuring system is within 20 throughout the frequency range of 2 to 30 mc where phase angle is measured for most of the commonly encountered line and source impedance values. For measurement of impedance magnitudes, the accuracy of the system is better than 20 for the range of the current-probes 100 kc to 100 mc.
APPROVED FOR PUBLIC RELEASE