Learn RF Spectrum Analysis Basics

Learn RF Spectrum Analysis Basics
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Learn RF Spectrum Analysis Basics

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    Jeff ThomasTom HolmesTerri HightowerLearn RF Spectrum Analysis Basics

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    Page 2Agenda• Overview: Spectrum analysis and its measurements• Theory of Operation: Spectrum analyzer hardware• Frequency Specifications• Questions and Answers break• Amplitude Specifications• Summary• Questions and Answers break

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    Page 3Learning Objectives• Name the major measurement strengths of a swept-tuned spectrum analyzer• Explain the importance of frequency resolution, sensitivity, and dynamic range in making analyzer measurements• Outline the procedure making accurate distortion measurements

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    Page 48563ASPECTRUM ANALYZER 9 kHz - 26.5 GHzOverview: What is Spectrum Analysis?

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    Page 5.ModulationModulationDistortionDistortionNoiseNoiseTypes of Tests Made

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    Page 6timeAmplitude(power)frequencyTime domainMeasurementsFrequency DomainMeasurementsFrequency Versus Time Domain

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    Page 7f1f2Fourier Spectrum Analyzer Fourier analyzer transforms a signal over time into a frequency spectrum DisplayAmplitudeFrequency

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    Page 8ff1f2Swept-Tuned Spectrum AnalyzerFilter “sweeps” over a frequency rangeDisplayAmplitudeFrequency

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    Page 9Agenda• Overview: Spectrum analysis and its measurements• Theory of Operation: Spectrum analyzer hardware• Frequency Specifications• Questions and Answers break• Amplitude Specifications• Summary• Questions and Answers break

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    Page 10FilterFrequencyReferenceLogAmpRF InputAttenuator MixerIF FilterDetectorVideoFilterLocalOscillatorSweepGeneratorIF GainInputDisplaySpectrum Analyzer Block Diagram

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    Page 11MIXERRFLOIFThe Mixer: Key to a Wide Frequency RangeInputRF = Radio frequencyLO = local oscillatorIF = intermediate frequencyfLOfin000fLO-finfLO+finfLO

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    Page 12IF FILTERInputIntermediate Frequency (IF) Filter• IF Bandwidth: also known as resolution bandwidth and RBW• Provides shape of frequency domain signal fDisplayedActualf

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    Page 13DETECTORNegative detection: smallestPositive detection: largestSample detection: lastAmplitudeInputDetectorValues Displayed

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    Page 14VIDEO FILTERInputWithout video filteringWith video filteringVideo Filter

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    Page 15LCD DISPLAYSWEEP GENLOfrequencyLocal Oscillator and Sweep Generator• Provides swept display

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    Page 16IF GAINRF INPUT ATTENUATORInput Attenuator and IF Gain Circuits• Protects input circuits• Calibrates signal amplitude• Keeps signal display position constant

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    Page 17Agenda• Overview: Spectrum analysis and its measurements• Theory of Operation: Spectrum analyzer hardware• Frequency Specifications• Questions and Answers break• Amplitude Specifications• Summary• Questions and Answers break

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    Page 18What Spectrum Analyzer Specifications are Important?• Frequency Range• Frequency and Amplitude Accuracy• Frequency Resolution• Sensitivity• Distortion• Dynamic Range

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    Page 19Frequency RangeLow frequencies for baseband and IFHigh frequencies for harmonics and beyond

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    Page 20Getting the Frequency Range You NeedLOMixerIF signal, fiffinfin Range01LO Range02fLO-finfLO+finfLO3fif1230 frequencyThe input signal is displayed when fLO -fin = fIF

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    Page 21Sweep generatorLOGetting the Frequency Range You Need0finfLO-fin fLO+finfLOfin Range01LO Range0234DisplayfifLO FeedthroughIF filter

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    Page 22LOGetting the Frequency Range You Need0finfLO-finfLO+finfLOfif34finfin Range01LO Range02Input signal displayed fLO -fin = fIF

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    Page 23Getting the Frequency Range You Need• Lower frequency limited by LO feedthrough• Upper frequency limited by LO range and IF frequency• Microwave frequency measurement usesharmonic mixing

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    Page 24AbsoluteAmplitudein dBmRelativeAmplitudein dBRelativeFrequencyFrequencyFrequency and Amplitude Accuracy

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    Page 25Frequency and Amplitude Accuracy•Frequency accuracy: −Internal/external frequency reference−Use of internal counter•Amplitude accuracy:−Not as good as a power meter−Dependent upon measurement procedure−Excellent relative measurements

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    Page 26Resolution BandwidthResidual FMNoise SidebandsWhat Determines Resolution?RBW Type and SelectivitySignal Resolution

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    Page 273 dB3 dB BWLOMixerIF Filter/Resolution Bandwidth Filter (RBW)SweepDetectorInputSpectrumDisplayRBWIF Filter Bandwidth

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    Page 283 dB10 kHz10 kHz RBWResolving Two Equal-level Signals

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    Page 293 dB60 dB60 dB BW60 dB BW3 dB BW3 dB BWSelectivity =Resolving Two Unequal-level Signals•3 dB bandwidth•Selectivity (filter shape)

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    Page 3010 kHzDistortionResolving Two Unequal-level Signals• For a RBW of 1 kHz and a selectivity of 15:1, the 60 dB bandwidth is 15 x 1 kHz = 15 kHz...• …so the filter skirt is 7.5 kHz away from the filter’s center frequency7.5 kHz60 dB

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    Page 31Residual FM"Smears" the SignalResidual FM

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    Page 32Noise Sidebands can prevent resolution of unequal signalsPhase NoiseNoise Sidebands (Phase Noise)

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    Page 33Penalty For Sweeping Too FastIs An Uncalibrated DisplaySwept too fastSweep Rate

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    Page 34SPAN 3 kHzRES BW 100 HzTypical SelectivityAnalog 15:1Digital 5:1Analog versus Digital Resolution BandwidthsAnalog FilterDigital Filter

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    Page 35Rules to Analyze By:Use the Analyzer’s Automatic Settings Whenever Possible • When using the analyzer in its preset mode, most measurements will be easy, fast, and accurate• Automatic selection of resolution bandwidth, video bandwidth, sweep time and input attenuation• When manuall...

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    Are There Any Questions?

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    Page 37Agenda• Overview: Spectrum analysis and its measurements• Theory of Operation: Spectrum analyzer hardware• Frequency Specifications• Questions and Answers break• Amplitude Specifications• Summary• Questions and Answers break

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    Page 38SweepLOMixerRFInputRES BWFilterDetectorA spectrum analyzer generates and amplifies noise just like any active circuit.Sensitivity and Displayed Average Noise Level

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    Page 3910 dBAttenuation = 10 dBAttenuation = 20 dB signal levelDisplayed noise is a function of RF input attenuationSignal-to-noise ratio decreases as RF input attenuation is increasedRF Input Attenuator Effects

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    Page 40Decreased BW = Decreased Noise100 kHz RBW10 dBDisplayed noise is a function of IF filter bandwidthIF Filter (Resolution Bandwidth) Effects10 kHz RBW1 kHz RBW10 dBBest sensitivity = narrowest RBW

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    Page 41Video BW smoothes noise for easier identification and measurement of low-level signalsVideo Bandwidth Effects

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    Page 42Signalequalsnoise~2.2 dBSensitivity - the smallest signal that can be measured

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    Page 43Rules to Analyze By:Getting the Best Sensitivity Requires Three Settings• Narrowest resolution bandwidth• Minimum RF attenuation• Sufficient video filter to smooth noise (VBW < 0.01 Resolution BW)

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    Page 44Resulting signalMixers Generate DistortionWhere is Distortion Generated?Signal to be measuredFrequency translated signalsMixer-generated distortion

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    Page 45Most Influential Distortion is the Second and Third OrderTwo-Toned IntermodHarmonic Distortion< -50 dBc< -50 dBc< -40 dBc

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    Page 46f2f3fPowerin dBDistortion Increases as a Function of the Fundamental’s Power∆ =1 dB ∆=2 dB∆=3 dBFundamental2nd Harmonic3rd HarmonicFor every dB fundamental level change,the 2nd changes 2 dB and the 3rd changes 3 dB.

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    Page 47How Distortion Amplitudes ChangeSince distortion changes relative to the fundamental, a graphical solution is practical.f2f3f1 dB/dBfund2 dB/dBfund∆ =1 dB ∆=2 dB∆=3 dB

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    Page 480-20-40-60-80-100-60-300+30.Third Order Intercept - TOISecondOrderThirdOrderPlotting Distortion as a Function of Mixer Level+5Distortion, dBcPower at the mixer =Input level minus the attenuator setting, dBm

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    Page 49Is the distortion from the signal or from the analyzer?No change in amplitude -distortion is part of input signal (external)Change Input Attenuation by 10 dB1Watch Signal on Screen:Change in amplitude - at least some of the distortion is being generated inside the analyzer (internal)IF GAI...

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    Page 50DynamicRangeDynamic Range -Optimum Amplitude Difference Between Large and Small Signals

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    Page 51.Displayed Noise Limits Dynamic RangeDistortion, dBc0-20-40-60-80-100-60-300+30Noise at 10 kHz RBWDisplayed average noise level can be plotted like distortion. 1 kHz RBWPower at the mixer =Input level minus the attenuator setting, dBm

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    Page 52..Maximum 2nd Order Dynamic RangeMaximum 3rd Order Dynamic RangeDynamic Range as a Function ofDistortion and Noise LevelDistortion and Signal-to-Noise, dBc0-20-40-60-80-100Power at the mixer =Input level minus the attenuator setting, dBm-60-300+30

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    Page 53Displayed Noise LevelClose-in Dynamic Range Limited by Noise Sidebands100 kHz to 1 MHzSideband NoiseDynamic Range Limited By Noise Sidebands, dBc/HzDynamic Range Limited By Distortion and Displayed Noise

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    Page 54Rules to Analyze by:Determining Dynamic Range• Internal second and/or third order distortion• Displayed noise level• Noise sidebands when close to large signalsYour spectrum analyzer’s dynamic range is dependent upon:

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    Page 55+30 dBm Maximum Power Level+10 dBm-45 dBm Second-order DistortionMixer Compression-35 dBm Third-order DistortionSignal/Noise Range 105 dBMeasurement Range 145 dBThird Order Distortion~80 dB0 dBc Noise SidebandsDynamic Range is Defined by Your ApplicationSecond Order Distortion~70 dBNoise S...

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    Page 56Summary• The RF spectrum analyzer is a heterodyne receiver• Offers a narrow resolution capability over a wide frequency range• Measures small signals in presence of large signals• Remember to:—Adjust the measurement procedure for specific application —Test for internal distorti...

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    Page 57Agilent Spectrum Analyzer Product Families - Swept TunedPSA SeriesHighest performance SA!3 Hz to 50 GHzPre-selection to 50 GHzWorlds best accuracy (0.24dB) 160 RBW settingsPhase noise optimizationFFT or swept at any RBWComplete set of detectorsFastest spur searchVector signal analysis.856X...

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    Page 58Agilent Vector Signal Analyzer Product Families89600 SeriesMulti-Format & Flexible vector signal analysisDC – 6.0 GHzBandwidth: 36 MHz RF, 40 MHz BasebandRF and modulation quality of digitalcommunications signals including WLAN.Spectrum & Time (FFT) AnalysisOFDM Analysis (802.11a...

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    Page 59FREE Agilent Email UpdatesFREE Agilent Email UpdatesSubscribe Today!Choose the information YOU want.Change your preferences or unsubscribe anytime. Go To:www.agilent.com/find/eseminar-emailKeep up to date on:Services and Support InformationEvents and Announcement- Firmware updates- New pro...