Keysight Technologies Spectrum Analysis Basics Application Note 150 Keysight Technologies. Inc. dedicates this application note to Blake Peterson. Blake’s outstanding service in technical support reached customers in all corners of the world during and after his 45-year career with Hewlett-Packard and Keysight. For many years, Blake trained new marketing and sales engineers in the “ABCs” of spectrum analyzer technology, which provided the basis for understanding more advanced technology. He is warmly regarded as a mentor and technical contributor in spectrum analysis. Blake’s many accomplishments include: –Authored the original edition of the Spectrum Analysis Basics application note and contributed to subsequent editions –Helped launch the 8566/68 spectrum analyzers, marking the beginning of modern spectrum analysis, and the PSA Series spectrum analyzers that set new performance benchmarks in the industry when they were introduced –Inspired the creation of Blake Peterson University––required training for all engineering hires at Keysight As a testament to his accomplishments and contributions, Blake was honored with Microwaves & RF magazine’s irst Living Legend Award in 2013. 2 Table of Contents Chapter 1 – Introduction ................................................................................................................ 5 Frequency domain versus time domain ....................................................................................... 5 What is a spectrum? ...................................................................................................................... 6 Why measure spectra? .................................................................................................................. 6 Types of signal analyzers ............................................................................................................... 8 Chapter 2 – Spectrum Analyzer Fundamentals .......................................................................... 9 RF attenuator .................................................................................................................................10 Low-pass filter or preselector ......................................................................................................10 Tuning the analyzer ......................................................................................................................11 IF gain .............................................................................................................................................12 Resolving signals ...........................................................................................................................13 Residual FM ...................................................................................................................................15 Phase noise ....................................................................................................................................16 Sweep time ....................................................................................................................................18 Envelope detector ........................................................................................................................20 Displays ..........................................................................................................................................21 Detector types ...............................................................................................................................22 Sample detection ..........................................................................................................................23 Peak (positive) detection ..............................................................................................................24 Negative peak detection ..............................................................................................................24 Normal detection ..........................................................................................................................24 Average detection .........................................................................................................................27 EMI detectors: average and quasi-peak detection ...................................................................27 Averaging processes .....................................................................................................................28 Time gating ....................................................................................................................................31 Chapter 3 – Digital IF Overview ..................................................................................................36 Digital filters ...................................................................................................................................36 All-digital IF....................................................................................................................................37 Custom digital signal processing ................................................................................................38 Additional video processing features .........................................................................................38 Frequency counting .....................................................................................................................38 More advantages of all-digital IF .................................................................................................39 Chapter 4 – Amplitude and Frequency Accuracy ......................................................................40 Relative uncertainty .....................................................................................................................42 Absolute amplitude accuracy ......................................................................................................42 Improving overall uncertainty ......................................................................................................43 Specifications, typical performance and nominal values .........................................................43 Digital IF architecture and uncertainties ....................................................................................43 Amplitude uncertainty examples .................................................................................................44 Frequency accuracy ......................................................................................................................44 3 Table of Contents continued Chapter 5 – Sensitivity and Noise ...............................................................................................46 Sensitivity .......................................................................................................................................46 Noise floor extension ....................................................................................................................48 Noise figure ....................................................................................................................................49 Preamplifiers ..................................................................................................................................50 Noise as a signal............................................................................................................................53 Preamplifier for noise measurements .........................................................................................54 Chapter 6 – Dynamic Range ........................................................................................................55 Dynamic range versus internal distortion ..................................................................................55 Attenuator test ...............................................................................................................................56 Noise ...............................................................................................................................................57 Dynamic range versus measurement uncertainty .....................................................................58 Gain compression .........................................................................................................................60 Display range and measurement range ......................................................................................60 Adjacent channel power measurements ....................................................................................61 Chapter 7 – Extending the Frequency Range ............................................................................62 Internal harmonic mixing .............................................................................................................62 Preselection ...................................................................................................................................66 Amplitude calibration....................................................................................................................68 Phase noise ...................................................................................................................................68 Improved dynamic range..............................................................................................................69