Understanding Spectrum & Signal Analysis
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Understanding Spectrum & Signal Analysis INTRODUCTION ............................................................................................................................... 4 Frequency Domain / Time Domain .................................................................................................. 6 SPECTRUM ANALYZERS .................................................................................................................. 8 Signal Analyzers ................................................................................................................. 9 Operation of each part..................................................................................................... 11 Traces................................................................................................................................. 17 Characteristics .................................................................................................................. 21 Frequency Range ............................................................................................. 21 Frequency Resolution ...................................................................................... 23 Sweep Speed ................................................................................................... 25 Sensitivity and Noise Figure ............................................................................ 25 Video Filtering or Averaging ........................................................................... 27 Signal Display Range ....................................................................................... 27 Dynamic Range ................................................................................................ 29 Frequency Accuracy ........................................................................................ 30 USES OF SIGNAL/SPECTRUM ANALYZERS ................................................................................. 30 APPLICATIONS ................................................................................................................................ 35 Amplitude Modulation .................................................................................................... 35 Modulation Frequency – fm ............................................................................ 40 Modulation Distortion ..................................................................................... 41 Frequency Modulation .................................................................................................... 43 Bandwidth of FM Signals ................................................................................................ 44 FM Measurements with a Spectrum Analyzer ............................................................... 46 AM Plus FM (Incidental FM) ............................................................................................ 49 Radio Signals .................................................................................................................... 51 Chirp Signals .................................................................................................................... 53 2-FSK Signals .................................................................................................................... 54 Frequency Hopping ......................................................................................................... 57 Noise ................................................................................................................................. 58 PULSE MEASUREMENTS ............................................................................................................... 61 Pulse Fundamentals ........................................................................................................ 63 Line Spectrum ................................................................................................................ 67 Pulse Spectrum ................................................................................................................ 69 Envelope Spectrum ......................................................................................................... 71 Pulse Desensitization - Peak Power Measurements ..................................................... 72 Average Power Measurements ...................................................................................... 76 2 Understanding Spectrum & Signal Analysis Burst Detect ...................................................................................................................... 78 Intermodulation Distortion ............................................................................................. 81 C/N Measurements ......................................................................................................... 83 Occupied Frequency Bandwidth ................................................................................... 84 Adjacent Channel Leakage Power ................................................................................. 86 Burst Average Power ....................................................................................................... 87 ERROR VECTOR MAGNITUDE (EVM) ........................................................................................... 88 EVM Troubleshooting ...................................................................................................... 90 EVM versus Time .............................................................................................................. 90 EVM Spectrum ................................................................................................................. 91 Dynamic EVM ................................................................................................................... 91 APPENDIX A Spectrum Analyzer Conversion Factors ......................................................................... 98 SWR – Reflection Coefficient – Return Loss ................................................................... 99 Power Measurement ..................................................................................................... 100 APPENDIX B Amplitude Modulation .................................................................................................. 101 APPENDIX C Frequency Modulation .................................................................................................. 104 Bessel Functions ........................................................................................................... 105 APPENDIX D Pulse Modulation ........................................................................................................... 106 APPENDIX E Intermodulation Distortion / Intercept Points ............................................................ 108 While careful attention has been taken to ensure the contents of this booklet are accurate, Anritsu cannot accept liability for any errors or omissions that occur. We reserve the right to alter specifications of products without prior notice www.anritsu.com 3 Introduction Background Rapid recent progress in development of wireless and broadcasting technologies, such as smartphones, wireless LAN, wireless sensor networks, RFID, GPS, digital TV, etc., has seen their widespread adoption in most people’s daily lives. A variety of measuring instruments, such as frequency counters, field strength meters, power meters, etc., is used to measure, analyze, and evaluate RF signals including electromagnetic (radio) waves broadcast by antennas; the spectrum analyzer plays a central role in detailed measurement, analysis, and evaluation of RF signals. The importance of the spectrum analyzer for engineers dealing with RF signals seems unlikely to change in the future. At the same time, progress in wireless communications technologies and the appearance of new applications have increased the complexity and level of the functions and performance required by spectrum analyzers. Among these requirements, the need to evaluate signals using new wideband digital modulation methods as well as to capture transient signal spectrums to troubleshoot problems with electromagnetic noise resulting from use of high sensitivity parts mounted at high densities requires new generations of spectrum analyzers using frequency sweep principles. As a result, the spectrum analyzer continues to evolve to meet the needs of engineers. As an example, the digitization of internal processing has led to huge jumps in measurement speed, accuracy and stability. As devices and computation speeds have become increasingly faster and more accurate, Anritsu has been incorporating developments in digital processing as signal analyzer functions into its MS2830A and MS2690A series. Such improvements not only support evaluation and analysis of digital modulation signals, but also support capture of various signals with non- regular spectrums. Figure 1 4 Understanding Spectrum & Signal Analysis Engineers and technicians involved in modern RF or microwave communications have many measuring instruments at their disposal, each designed for specific measurement tasks. Among those available are: a) The Oscilloscope – primarily developed for measuring and analyzing signal amplitudes in the time domain. (Voltage vs. time) Often 2, 4 or more channels of voltage vs. time can be viewed on the same display to show the relationships between signals. Extensive methods to