Spectrum Analysis Basics CMB 12/96 1 What is the Difference Between Network and Spectrum Analyzers?....

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1Spectrum Analysis BasicsCMB 12/96

What is the Difference Between Network and Spectrum Analyzers?

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Am

plit

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Frequency

Am

plit

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Frequency

8563A

SPECTRUM ANALYZER 9 kHz - 26.5 GHz

Measures known signal

Measures unknown signals

Network analyzers: measure components, devices,

circuits, sub-assemblies contain source and receiver display ratioed amplitude and

phase(frequency or power sweeps)

offer advanced error correction

Spectrum analyzers: measure signal amplitude

characteristicscarrier level, sidebands, harmonics...)

can demodulate (& measure) complex signals

are receivers only (single channel) can be used for scalar component test

(nophase) with tracking gen. or ext. source(s)

4Spectrum Analysis BasicsCMB 12/96

OverviewTypes of Tests Made

ModulationModulation

DistortionDistortion

NoiseNoise

5Spectrum Analysis BasicsCMB 12/96

OverviewFrequency versus Time Domain

time

Amplitude

(power)frequency

Time domainMeasurement

s

Frequency DomainMeasurements

7Spectrum Analysis BasicsCMB 12/96

OverviewDifferent Types of Analyzers

A

ff1 f2

Filter 'sweeps' over range of interest

CRT shows full spectral display

Swept Analyzer

9Spectrum Analysis BasicsCMB 12/96

Theory of OperationSpectrum Analyzer Block Diagram

Pre-SelectorOr Low Pass

Filter

CrystalReferenc

e

LogAmp

RF inputattenuato

r mixer

IF filterdetecto

r

video

filterlocaloscillato

r sweepgenerato

r

IF gain

Inputsigna

l

CRT display

10Spectrum Analysis BasicsCMB 12/96

Theory of OperationMixer MIXER

fsig

LOf

fsig LOf

LOf fsig-LOf fsig+RF

LOIF

input

11Spectrum Analysis BasicsCMB 12/96

Theory of OperationIF Filter IF FILTER

Display

InputSpectru

mIF Bandwidth

(RBW)

12Spectrum Analysis BasicsCMB 12/96

Theory of OperationDetector DETECTOR

Negative detection: smallest value in bin displayed

Positive detection: largest value in bin displayed

Sample detection: last value in bin displayed

"bins"

amplitude

13Spectrum Analysis BasicsCMB 12/96

Theory of OperationVideo Filter

VIDEO FILTER

14Spectrum Analysis BasicsCMB 12/96

Theory of OperationOther Components

CRT DISPLAY

SWEEP GEN

LO

IF GAIN

frequency

RF INPUT ATTENUATOR

15Spectrum Analysis BasicsCMB 12/96

Theory of OperationHow it all works together

3.6

(GHz)

(GHz)

0 3 61 2 4 5

0 31 2

3 64 5

3.6

(GHz)0 31 2

fIF

Signal Range

LO Range

fs

sweep generator

LO

CRT display

input

mixer

IF filter

detector

A

f

fLO

fs

fs

fs

fLO

-f

sf

LO+

fLO

3.6

6.5

6.5

39Spectrum Analysis BasicsCMB 12/96

SpecificationsSensitivity/DANL

10 dB

Attenuation = 10 dB Attenuation = 20 dB

signal level

Effective Level of Displayed Noise is a Function of RF Input Attenuation

Effective Level of Displayed Noise is a Function of RF Input Attenuation

Signal-To-Noise Ratio Decreases as RF Input Attenuation is Increased

40Spectrum Analysis BasicsCMB 12/96

SpecificationsSensitivity/DANL: IF Filter (RBW)

Decreased BW = Decreased Noise

100 kHz RBW10 kHz RBW1 kHz RBW

10 dB10 dB

Displayed Noise is a Function of IF Filter Bandwidth

Displayed Noise is a Function of IF Filter Bandwidth

41Spectrum Analysis BasicsCMB 12/96

SpecificationsSensitivity/DANL: VBW

Video BW Smoothes Noise for Easier Identification of Low Level

Signals

Video BW Smoothes Noise for Easier Identification of Low Level

Signals

43Spectrum Analysis BasicsCMB 12/96

SpecificationsSensitivity/DANL

Narrowest Resolution BW

Minimum RF Input Attenuation

Sufficient Video Filtering(Video BW < .01 Res BW)

For Best Sensitivity Use:For Best Sensitivity Use: