Progress in Modern EMI Test Instrumentation

The paper describes the efficient use of microprocessor intelligence in test receivers for the detection and analysis of EMI. Progress in hardware, especially in synthesized local oscillators is accompanied by a corresponding progress in firmware. The process of concentrating computing intelligence closer to the analog hardware has continued. Work that has previously been the task of an external controller will in future be done by the test receiver itself. The result is a compact, intelligent and flexible system. Test receivers will no longer only scan the input spectrum but will also be able to analyze it and compare it to the specification limits. The paper treats strategies for optimum signal detection and it will show that flexibility is needed for different situations. In cases where quasi peak and average limits have to be taken into consideration a prescan may be done with a peak and an average detector at the same time. The critical points of the EMI spectrum may automatically be extracted for time consuming tests like quasi peak weighting. The simultaneous use of the peak detector with a weighting detector in conjunction with the microprocessor firmware helps to optimize autoranging procedures with weighting detectors like average and quasi peak. Even for manual use of test, receivers without a spectrum display the microprocessor can give the user the necessary orientation aid. Besides that the test receiver's I/O interfaces can control the most important coupling devices, the antenna mast and EuT turntable and it will be enabled to produce the complete test reports and to save test results. In other words: the test receiver will be self-contained.