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Agilent PN 89400-14 Using Error Vector Magnitude Measurements to Analyze and Troubleshoot Vector-Modulated Signals Product Note Error vector magnitude (EVM) measurements Vector signal analyzers such as the Agilent 89400 can provide a great deal of insight into the per- perform the time, frequency, and modulation domain analyses that provide these insights. Because they formance of digitally modulated signals. With process signals in full vector (magnitude and phase) proper use, EVM and related measurements form, they easily accommodate the complex modu- can pinpoint exactly the type of degradations lation formats used for digital RF communications. present in a signal and can even help identify Perhaps most importantly, these analyzers contribute their sources. This note reviews the basics of a relatively new type of measurement called "error EVM measurements on the Agilent Technologies vector magnitude," or EVM. 89400 vector signal analyzers, and outlines a Primarily a measure of signal quality, EVM pro- general procedure that may be used to methodi- vides both a simple, quantitative figure-of-merit cally track down even the most obscure signal for a digitally modulated signal, and a far-reaching problems. methodology for uncovering and attacking the underlying causes of signal impairments and dis- The diverse technologies that comprise today's dig- tortion. EVM measurements are growing rapidly ital RF communications systems share in common in acceptance, having already been written into one main goal: placing digital bit-streams onto RF such important system standards as GSM1, NADC 2, carriers and then recovering them with accuracy, and PHS 3, and they are poised to appear in several reliability, and efficiency. Achieving this goal demands upcoming standards, including those for digital engineering time and expertise, coupled with keen video transmission. This note defines error vector insights into RF system performance. magnitude and related measurements, discusses how they are implemented, and explains how they are practically applied in digital RF communica-