SEMINAR
ON
SPECTRUM ANALYZER
By: Dr. Deepak Garg
Mr. Alok Kumar Singh
ELECTRONICS & COMMUNICATION ENGINEERING DEPARTMENT
CONTENTS OF PRESENTATION
• What is Spectrum Analyzer (SA)
• Classification of SA on the basis of form factors
• Classification of SA on the basis of the methods used to
obtain the spectrum of a signal.
• Brief Idea about each type of SA and advantages &
disadvantages.
• Specifications of SA
• Basics of Tracking Generator
• Applications of SA in different areas
What is Spectrum analyzer
• A spectrum analyzer measures the magnitude of an input signal
versus frequency within the full frequency range of the
instrument.
• The primary use is to measure the power of the spectrum of
known and unknown signals.
• The input signal that a spectrum analyzer measures is electrical,
however, spectral compositions of other signals, such as acoustic
pressure waves and optical light waves, can be considered
through the use of an appropriate transducer.
• By analyzing the spectra of electrical signals, dominant frequency,
power, distortion, harmonics, bandwidth, and other spectral
components of a signal can be observed that are not easily
detectable in time domain waveforms.
• Spectrum analyzers are widely used within the electronics
industry for analyzing the frequency spectrum of radio frequency,
RF and audio signals.
Why Spectrum Analysis
• Any waveform seen in the time domain, there is an equivalent
representation in the frequency domain.
• Any signal is made up from a variety of components of different
frequencies.
• By being able to look at signals in the time domain provides many
advantages and in particular for RF applications.
• Looking at signals in the frequency domain with a spectrum
analyzer enables aspects such as the harmonic and spurious
content of a signal to analyzed, the width of signals when
modulation has been applied etc. these aspects are of particular
importance for developing RF signal sources, and especially any
form of transmitter including those in cellular, Wi-Fi, and other
radio or wireless applications.
• To monitor the radiation of unwanted signals causing interference
to other users of the radio spectrum, and to ensure such
unwanted signals are kept below an acceptable level.
SA Display
• An analyzer display, like that of an
oscilloscope has two axes. For the
spectrum analyzer the vertical axis
displays level or amplitude, whereas
the horizontal axis displays frequency.
• The name indicates analyses the
spectrum of a signal. It shows the
relative levels of signals on different
frequencies within the range of the
particular sweep or scan.
• The vertical or amplitude axis is
normally on a logarithmic scale and is
calibrated in dB in line with many other
measurements that are made for signal
amplitudes.
• The horizontal scale conversely is
normally linear. This can be adjusted to
cover the required range. The term
span is used to give the complete
calibrated range across the screen.
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
Classification & Features of SA
(A) On the basis of Form Factor
Spectrum analyzers tend to fall into four form factors:
(i) Benchtop
(ii)Portable
(iii)Handheld and
(iv) Networked.
Benchtop
• Generally means for a lab environment or production/ manufacturing area.
• Have better performance and specifications than the portable or handheld form
factor.
• Some bench top spectrum analyzers offer optional battery packs, allowing them
to be used away from AC power.
Portable
• Used when SA needs to be taken outside to make measurements or simply
carried while in use.
• Optional battery-powered
• Clearly viewable display
• Light weight
Features of Form Factor based
SA
Handheld
• Useful for application where the spectrum analyzer needs to be very light and small.
• Handheld analyzers offer a limited capability
• Very low power consumption.
• Battery-powered operation
• Very small size
• Light weight
Networked
• A new class of geographically-distributed spectrum monitoring and analysis
applications.
• The key attribute is the ability to connect the analyzer to a network and monitor
such devices across a network.
• Key applications for such devices include RF intrusion detection systems for secure
facilities where wireless signaling is prohibited.
• Cellular operators are using such analyzers to remotely monitor interference in
licensed spectral bands.
• Network-efficient data transfer
• Low power consumption
• The ability to synchronize data captures across a network of analyzers
• Low cost to enable mass deployment.
Pictures of SA
RF Spectrum Analyzer
• Agilent Technologies 9 kHz to 3 GHz, 10 Hz minimum
resolution bandwidth
Spectrum Analyzer Display
(B) On the basis by the methods used to obtain the spectrum of a signal.
Spectrum analyzers tend to fall into four types: (i) Swept or superheterodyne spectrum analyzers: Based on the use of the
super heterodyne principle, sweeping the frequency that is analyzed across
the required band to produce a view of the signals with their relative
strengths and is most widely used.
(ii) Fast Fourier Transform, FFT analyzers: Use a form of Fourier transform,
Fast Fourier Transform(FFT) converting the signals into a digital format for
analysis digitally. These are more expensive and ore specialized
(iii)Real-time analyzers: These are a form of FFT analyzer, they offer their
results instantaneously, i.e. in real-time.
(iv)Audio spectrum analyzer: Audio spectrum analyzers are focused, on
audio frequencies, and this means that low frequency techniques can be
adopted. This makes them much cheaper. It is even possible to run them on
PCs with a relatively small amount of hardware.
Sweep Spectrum Analyzer
Advantages, Disadvantages & APPS of
SSA
Advantages
• Able to operate over wide frequency range
• Wide bandwidth: Have very wide scan spans. These may
extend to several GHz in one scan.
• Not as expensive as other spectrum analyzer technologies:
Disadvantages
• Cannot measure phase: It is a scalar instrument and unable
to measure phase, can only measure the amplitude of signals
on given frequencies.
• Cannot measure transient events: It sweeps the bandwidth
required, this takes longer and as a result it is unable to
capture transient events effectively.
Applications
• It offers excellent performance for the majority of RF test
equipment applications.
FFT Spectrum Analyzer
Advantages and Disadvantages of
FFT SA
Advantages
• Fast capture of waveform: The waveform is analysed digitally, hence it can
be captured in a relatively short time.
• Able to capture non-repetitive events: The short capture time means that
the FFT analyzer can capture non-repetitive waveforms.
• Able to analyze signal phase: Data can be processed to reveal the phase of
signals.
• Waveforms can be stored: It is possible to capture the waveform and
analyze it later when it is required.
Disadvantages
• Frequency limitations: The main limit of the frequency is ADC that is used
to convert the analogue signal into a digital format, this component still
places a major limitation on the upper frequency limits.
• Cost: The ADC is a very high cost item, in addition to all the other
processing and display circuitry required, this results in the costs rising for
these items.
Real Time SA
• Can acquire a particular bandwidth or span either side of a center
frequency.
• Captures all the signals within the bandwidth and analyses them in real
time.
• Real Time SA captures the waveform in memory and then uses a fast
Fourier transform technology to analyze the waveform very quickly, i.e. in
real-time.
• By analyzing the waveform in this way, transient effects can be captured
and highlighted.
• They are based around an FFT - Fast Fourier Transform spectrum analyzer.
• Have a real-time - very fast - digital signal processing engine capable to
processing the entire bandwidth with no gaps.
• An ADC capable of digitizing the entire bandwidth of the pass band.
• Sufficient capture memory to enable continuous acquisition over the
desired measurement period.
Specifications of SA
• Spectrum analyser specifications are used to determine whether a particular test
instrument will be able to meet the requirements placed upon it.
• There are several different specifications, each detailing different aspects of the
performance of the instrument: Frequency coverage
• It is necessary to consider the maximum frequencies that will need to be viewed.
The frequency range must be such that harmonics of the fundamental and other
important spurious signals can be viewed.
• To achieve this the analyzer frequency range must extend well beyond the
fundamental frequency of the signal. Often the figure used is ten times that of the
fundamental, although often it is necessary to settle for top frequencies of less than
this.
Amplitude accuracy
• The amplitude accuracy is a major spectrum analyzer specification.
• The amplitude accuracy specification of a spectrum analyzer is determined by a
number of factors, including the basic accuracy of the instrument as well as its
frequency response
• The spectrum analyzer has a special power sensor that calibrates the input level at a
number of absolute level points.
Frequency accuracy specification
• Most SA today employ frequency synthesized sources. This means that the accuracy
of the frequency measurement is governed by that of the peak detection circuitry,
detecting where the center of a signal is, and also the accuracy of the reference
source within the frequency synthesizer.
Spectrum analyzer sensitivity specification
• In order to determine the low signal performance of spectrum analyzer a
sensitivity specification is normally given. This is normally specified in terms of
dBm / Hz at a given frequency.
• If a noise figure specification is required, then this can be calculated:
Noise Figure = Sensitivity (dBm/Hz) - Noise floor at room temp (-174 dBm/Hz)
Phase noise specification
• There are many instances when the phase noise of a signal source, e.g. a
transmitter, receiver local oscillator, etc needs to be measured. When this is the
case, the phase noise specification of the spectrum analyzer is of particular
importance.
Spectrum analyzer dynamic range
• Dynamic range is a particularly important parameter for any spectrum analyzer. It
is required to look at signals with enormously wide level ranges. Therefore the
ability of the spectrum analyzer to accurately look at small signals in the presence
of relatively close strong signals is particularly important.
Tracking Generator
• The tracking generator enables some basic network measurements to be
made, providing additional capability beyond basic spectrum analysis.
• A tracking generator considerably extends the applications making SA’s
more flexible and versatile.
• In their basic form, analyzers are not able to make response or network
measurements. In order to make a network measurement like this, it is
necessary to have a source to stimulate the device under test, and then a
receiver is needed to measure the response.
• This makes possible for a variety of network measurements including
frequency response, conversion loss, return loss etc..
• There are two items of test equipment RF network analyzer and the other
is a spectrum analyzer with a tracking generator that can be used to make
stimulus-response measurements
• For phase information a vector network analyzer is used, but for many
other network measurements a spectrum analyzer tracking generator
arrangement can be used at no additional cost.
Block Diagram of TG
Applications Of SA
Widely used to measure :
• Frequency response, noise and distortion characteristics of all kinds of
RF circuitry, by comparing the input and output spectra.
• In telecommunications they are used to determine occupied
bandwidth and track interference sources. For example, cell planners
use this equipment to determine interference sources in the GSM
frequency bands and UMTS frequency bands.
• In EMC, it is used for basic pre-compliance testing; however, it can not
be used for full testing and certification. Instead, an EMI receiver is
used.
• Used to determine whether a wireless transmitter is working
according to federally defined standards for purity of emissions.
• Also used to determine, by direct observation, the bandwidth of
a digital or analog signal.
Continued….
• Connects to a wireless receiver or a personal computer to allow visual
detection and analysis of electromagnetic signals over a defined band of
frequencies. This is called panoramic reception and it is used to
determine the frequencies of sources of interference to wireless
networking equipment, such as Wi-Fi and wireless routers.
• Used to assess RF shielding (RF shielding is of particular importance for
the siting of a magnetic resonance imaging machine since stray RF fields
would result in artifacts in an MR image.)
• Used at audio frequencies to analyze the harmonics of an audio signal,
for eg. measure the distortion of a nominally sinewave signal.
• An optical spectrum analyzer uses reflective and/or refractive techniques
to separate out the wavelengths of light.
Any Queries!!