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

1Spectrum Analysis BasicsCMB 12/96

What is the Difference Between Network and Spectrum Analyzers?

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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)


OverviewTypes of Tests Made

ModulationModulation

DistortionDistortion

NoiseNoise


OverviewFrequency versus Time Domain

time

Amplitude

(power)frequency

Time domainMeasurement

s

Frequency DomainMeasurements


OverviewDifferent Types of Analyzers

A

ff1 f2

Filter 'sweeps' over range of interest

CRT shows full spectral display

Swept Analyzer


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


Theory of OperationMixer MIXER

fsig

LOf

fsig LOf

LOf fsig-LOf fsig+RF

LOIF

input


Theory of OperationIF Filter IF FILTER

Display

InputSpectru

mIF Bandwidth

(RBW)


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


Theory of OperationVideo Filter

VIDEO FILTER


Theory of OperationOther Components

CRT DISPLAY

SWEEP GEN

LO

IF GAIN

frequency

RF INPUT ATTENUATOR


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


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


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


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


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:

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

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