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Spectrum- Analyzer

Course

Pengukuran Elektronika (PTE17056)

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Universitas Islam Negeri Ar-Raniry

Academic year: 2022/2023

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Widener University

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Spectrum Analyzer

INTRODUCTION

▪ A spectrum in the practical sense is a collection of sine waves , when combined properly produces the required time domain signal. ▪ The frequency domain also has its measurement strengths. ▪ The frequency domain is better for determining the harmonic content of a signal. time Amplitude (power) frequency Time domain Measurements Frequency Domain Measurements

Analog & Digital

▪ An analog spectrum analyzer uses either a variable bandpass filter whose mid-frequency is automatically tuned (shifted, swept) through the range of frequencies of which the spectrum is to be measured or a superheterodyne receiver where the local oscillator is swept through a range of frequencies. ▪ A digital spectrum analyzer computes the Fast Fourier transform (FFT), a mathematical process that transforms a waveform into the components of its frequency spectrum

Spectrum Analysis

▪ In various field operations involving signals there is need to ascertain the nature of the signal at several points. ▪ Signal characteristics affect the parameters of operation of a system. ▪ Spectrum analysis mostly involves study of the signal entering a system or that produced by it. ▪ Spectrum analyzers usually display raw, unprocessed signal information such as voltage, power, period, waveshape, sidebands, and frequency. They can provide you with a clear and precise window into the frequency spectrum.

FFT Spectrum Analyzer

THE MEASUREMENT SYSTEM ▪ The analyzer is looking at the entire frequency range at the same time using parallel filters measuring simultaneously. ▪ It is actually capturing the time domain information which contains all the frequency information in it. ▪ With its real-time signal analysis capability, the Fourier analyzer is able to capture periodic as well as random and transient events. ▪ It also can provide significant speed improvement over the more traditional swept analyzer and can measure phase as well as magnitude.

Swept Spectrum Analyzer

▪ Very basically, these analyzers "sweep" across the frequency range of interest, displaying all the frequency components present. ▪ The swept-tuned analyzer works just like the AM radio in your home except that on your radio, the dial controls the tuning and instead of a display, your radio has a speaker. ▪ The swept receiver technique enables frequency domain measurements to be made over a large dynamic range and a wide frequency range. ▪ It has significant contributions to frequency-domain signal analysis for numerous applications, including the manufacture and maintenance of microwave communications links, radar, telecommunications equipment, cable TV systems, and broadcast equipment; mobile communication systems;

EMI diagnostic testing; component testing; and signal surveillance.

▪ The major components in a spectrum analyzer are the ▪ RF input attenuator, mixer, ▪ IF (Intermediate Frequency) gain, ▪ IF filter, detector, ▪ video filter, ▪ local oscillator, ▪ sweep generator ▪ CRT display.

Theory of Operation

Mixer

MIXER fsig f LO fsig fLO f LO - fsig f LO fsig + RF LO IF

####### input

Theory of Operation

IF Filter IF FILTER

Display Input Spectrum IF Bandwidth (RBW)

IF FILTER

▪ The IF filter is a bandpass filter which is used as the "window" for detecting signals. ▪ It's bandwidth is also called the resolution bandwidth (RBW) of the analyzer and can be changed via the front panel of the analyzer. ▪ By giving a broad range of variable resolution bandwidth settings , the instrument can be optimized for the sweep and signal conditions, letting trade-off frequency selectivity (the ability to resolve signals), signal-to-noise ratio (SNR), and measurement speed. ▪ As RBW is narrowed, selectivity is improved (we are able to resolve the two input signals). This will also often improve SNR.

Continued...

▪ In sample detection mode, a random value for each "bin" of data (also called a trace element) is produced. This detector mode is best for computing the rms value of noise or noise-like signals, but it may miss the peaks of burst signals and narrowband signals when the RBW is narrower than the frequency spacing of the bins. ▪ For displaying both signals and noise, a detector mode called the normal detector mode

DETECTOR

▪ The analyzer must convert the IF signal to a baseband or video signal so it can be viewed on the instrument's display. This is accomplished with an envelope detector which then deflects the CRT beam on the y-axis, or amplitude axis. ▪ Many modern spectrum analyzers have digital displays which first digitize the video signal with an analog-to-digital converter (ADC). ▪ The positive-peak detector mode captures and displays the peak value of the signal over the duration of one trace element ▪ The negative-peak detector mode captures the minimum value of the signal for each bin.