Tektronix - Real-Time Spectrum Analysis for EMI Diagnostics

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This application note briefly examines the different stages of design and test with respect to test equipment and measurement techniques. It also reviews the currently-specified detection and filtering methods, and provides a quick reference to the specified measurement bands and their associated filters and detectors. Finally, an example of EMI diagnostics is given, using the unique DPX spectrum display for discovery and the frequency mask trigger for signal capture.


From the first wireless transmissions, electromagnetic interference (EMI) has been a concern for design engineers. The earliest spark-gap transmitters had no facility for spectrum control, and the presence of two transmitters in proximity caused interference in the receivers. These first transmissions were ‘one-to-one’ in that a single transmitter was communicating with a single receiver, and the information was in digital form, that is, Morse code using on-off keying (OOK). As more companies entered the field of wireless communications, regulation of the bands used was accomplished by negotiation between these competitors. This led to more efficient modulation techniques, frequency allocations and receivers with better selectivity. As electronics progressed, it became possible to send voice and video in analog form, and the transmissions became one-tomany broadcasts. This led to the need both to partition the broadcast bands for exclusive use by licensed carriers, and the need to regulate devices that might interfere with these transmissions. Now we have come full-circle: transmissions are once again digital in nature, and may be required to manage their own interference, as is the case in ultra-wideband (UWB) systems and the many proliferating systems in the unlicensed Industrial, Scientific and Medical (ISM) band including Bluetooth, WLAN and others. In the licensed bands, we have cellular, satellite, broadcast and other systems creating a complex, dynamic spectrum environment. At the same time, other systems, such as computer, electronic and electrical machinery have exploded in popularity, increasing the probability of interference...

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