Measurement parameter evaluation for prescans as part of radiated EMI measurements

Preliminary field strength measurements, also known as prescans, are an integral part of most radiated EMI measurements and serve a number of different purposes. In almost all applications, these type of tests are used to quickly obtain information about the frequency spectrum emitted by the equipment under test (EUT). In order to minimize measurement time, peak detection is usually used instead of quasi-peak or average detection which is called out in most commercial EMI regulations. A measurement system consisting of a swept EMI receiver with a real-time display, dedicated control software, and necessary accessories is best suited for this task. It rapidly acquires spectral information, provides both graphical and tabular representation of test results and gives an insight to characteristics of emissions from the EUT. Achieving the highest measurement speed is one of the most important goals when executing prescans. However, there are tradeoffs to be made which might affect frequency uncertainty, receiver display frequency resolution, display detection mode, antenna tower and turntable movement. This paper discusses the significance of these test parameters for prescan and their impact on measurement time and efficiency.