Spectrum Analyzer

Another Oscilloscope???

Like an oscilloscope

Oscilloscope in time domain

Spectrum analyzer in frequency domain (selectable)

Is Frequency Domain Better?

In time domain, all frequency components of signals are summed together

In freq domain, complex signals are separated into their frequency components

What does SA do?

Processes the signal Displays the spectral content of the input

signal within a selected range of frequencies i.e., signal power(db) versus frequency Measures frequency, power, harmonic

content, modulation, spurs, and noise, etc…

Types of RF Spectrum Analyzer

Two common ways to measure RF signals Fourier Transform Swept-Tuned or Swept-Toned

Fourier Analyzer

Capture time domain signals information Digitizes time domain signal (digital

sampling) Perform Fourier transform Fast, but limits in frequency range, sensitivity

Swept Analyzer

“Sweep” across frequency range Display the frequency of interest Large frequency range Widely used

RF Spectrum Analyzer

ADVANTEST 9 kHz to 3 GHz, 1 kHz resolution

Three Primary Function Keys

Frequency (Hz) Amplitude (Abs dBm, Rel dB) Span (Hz) -> (how big the “window” we want to

view)

Other Important Keys

Resolution BandwidthVideo Bandwidth

Peak Search Marker

Save

Auto Tune

Softkeys

Typical Output Displayed

04/18/23

The TDS-220 Tektronix Oscilloscope and the

FFT module

Functions

An instrument for observing a waveform both in time and frequency domains

In time domain works as a digital oscilloscope

MeasureCursorMain Keys

Volts/Div Sec/DivMath

Autoset

Frequency Domain

Takes the FFT of a waveform The FFT samples relate to the DTFS samples,

i.e., Takes a portion of a signal and repeats it

sak '

Taking FFT

There 4 steps to take the FFT 1. Setting up the time-domain waveform

• Use AUTOSET to display the proper YT waveform• Need to see a few periods of the waveform clearly

Good scale Bad scale

Taking FFT

• Be careful about the DC values

2. Press the MATH key to see the FFT menu• Use the FFT CH1/2 to switch between the

channel ½ FFT and YT waveforms

Taking FFT

3. Choose the window type • Choose the HANNING window for measurements

Point by pointmultiplication X =

Taking FFT

4. Use FFT Zoom menu to zoom • The left graticule line is at 0Hz frequency

Measurements Scales

Measurements on FFT waveforms• Frequency in Hz from 0Hz to half of the sampling

rate• Magnitude in dB where 0dB equals 1 V RMS

dB and dBm dB a relative value dBm an absolute value when the reference power is

1mW

References

Basic Spectrum Analyzer (HP) Knowing The Signal Classes Greatly

Simplifies Spectrum Analysis (TestMart) Signal Processing

http://www.ece.queensu.ca/hpages/courses/Elec421/why.html

TDS200 Series Digital Real-Time Oscilloscope, User Manual (Tektronix)

TDS200 Series Extension Modules, Instruction Manual (Tektronix)