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Agilent PN 89400-8 Using Vector Modulation Analysis in the Integration, Troubleshooting, and Design of Digital RF Communications Systems Product Note Introduction The Agilent Technologies 89400 Series vector signal analyzers (VSAs) with vector modulation analysis (Option AYA) provide the numerical and visual tools to help quickly identify and quantify impairments to digitally modulated signals, whether using standard or several nonstandard modulation formats. Measurements are possible on continuous or burst carriers (such as TDMA) at baseband, IF, and RF locations throughout a system block diagram. There is no need for external filtering, coherent carrier signals, or symbol clock tint- ing signals. The 89400 Series VSAs with Option AYA have built-in Gaussian, raised-cosine, root-raised-cosine, and user-definable filters (with adjustable alpha or BT) and lock to the carrier and a defined symbol rate. Although it is useful to measure the signal being transmitted, imagine the ben- efit of being able to detect, quantify, and locate the errors in the transmitted signal when compared to an ideal reference signal. Common vector modulation analysis tools such as eye and constellation displays are supported as well as new analysis tools including the ability to compare measured signals to ideal signals. Measurements update as fast as two times per second, allowing the effects of changes to an active system to be quickly analyzed. Advanced spec- trum analysis rounds out the 89400 Series VSAs' measurement contributions (additional information is in the reference list). By reducing the amount of external equipment or the need for developing custom solutions, accuracy is preserved and system development time can be simplified and minimized. Basic vector modulation and measurement concepts are presented, followed by example measurements and setups. A transmitter system is used as the foun- dation for the measuements; however, any system with I and Q signals can use the principles and tools presented. These applications are intended to serve as examples of the measurement power and ease of use of the analyzer. Contents 1 Introduction 2 Background 3 Modulation concepts 4 Measurement concepts 8 Problems that can occur during transmission, integration, and design 9 Identifying problems: Using measurements and display tools 15 Setting up the measurements 20