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 Bandwidth Video Bandwidth Peak Search Marker Save Auto Tune Softkeys

Typical Output Displayed

6/3/2015 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

Measure Cursor Main Keys Volts/Div Sec/Div Math 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

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 point multiplication 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 TDS200 Series Digital Real-Time Oscilloscope, User Manual (Tektronix) TDS200 Series Extension Modules, Instruction Manual (Tektronix)