Evaluation Engineering - 14

SIGNAL/SPECTRUM ANALYZERS

provides excellent flexibility for this type
of environment."
Stinson, Tektronix: "Ruggedized, portable
systems for field and range testing applications; Increased channel counts are
of related importance to many customers; Recording capabilities that enable
extended logging of real-time RF data
at high bandwidths; Advanced triggers
that allow real-time spectrum analyzers to detect spurious, intermittent, or
anomalous signals that swept-tuned
instruments will miss."
Sanchez and Nilsson, Rohde & Schwarz:
"There is a general need for wider analysis
bandwidths that go up to the GHz range,
especially in radar and satellite applications. A good example is the flexibility
to work with any kind of stimulus signals when characterizing components
or systems in the aerospace industry.
Customers that only tested with CW
signals in the past are now working with
digitally modulated signals, for example,
when measuring error vector magnitude,
etc. As always, features that automate
measurements are in high demand."
Smith, RADX: "Built-in RF record capabilities so an external recorder is not required; RTSAs with more demodulation
and analysis capabilities; Ability to zoom
into a region to look for small amplitude,
frequency-agile signals."

Advantages/disadvantages
of configuration
Spectrum and signal analyzers come in
a variety of configurations, such as traditional benchtop instruments, handheld instruments with display, USB instruments,
and PXI modules. What do vendors see as
the advantages and disadvantages of each?
Belleau, Anritsu: "There is a continuing
trend towards USB instruments, in particular. They bring a cost-effective advantage
since they do not require the internal microprocessor, memory, display, and so on.
USB instruments are generally extremely
portable, and many make direct connections to the device under test, which
eliminates errors caused by cables, etc. PXI

14

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modules, and variations of PXI modules,
also offer some advantages, particularly in
cases where multiport, simultaneous measurements are required. They do typically
require a mainframe chassis, which makes
them somewhat challenging to be moved
from one location to another. Due to the
physical form factor of the PXI module
itself, there are often performance tradeoffs in order to have the product fit within
its constraints. Traditional benchtop instruments are gradually being replaced by
these more modern USB and PXI equivalents, although for absolute highest performance requirements, benchtop analyzers
are still required and will continue to be
until such time that the USB or PXI based
instruments are able to fully match the
performance of the benchtop instruments."
Chonko, SIGLENT: "Benchtop instruments generally deliver the best performance for the investment. This is mainly
due to the heavy use of high-volume parts
in their designs. Handhelds are very useful
for field measurements, but they are usually higher cost with lower performance,
due to the design challenges and more
specific components required for batterypowered operation. USB instruments offer
the lower cost and higher performance
of a benchtop instrument in a somewhat
more portable form factor, but they require a computer, software, and ultra-fast
USB connection for full performance. PXI
instruments and other modular products
are very similar to benchtop instrumentation, but they don't have displays or the
ability to operate "on their own." They
require a somewhat costly mainframe
and controlling computer. They are very
well suited to fixed installation tests in
manufacturing or long-term R&D tests."
Sanchez and Nilsson, Rohde & Schwarz:
"While modular architecture may appear
cost-efficient at first, there are hidden
expenses for customers in terms of additional software development, training,
and application support. Additionally, the
suppliers of PXI modules do not always
provide specifications that are thorough
enough. A majority of customers prefer
benchtop instruments. They are easier to
configure, customers can start making

measurements right away, and integration in measurement systems can be done
easily via GPIB or LAN."

Multifunction vs. dedicated instrument
Today, digital oscilloscopes can perform
fast fourier transforms (FFTs), and many
now have dedicated spectrum-analyzer
channels. What are the advantages and
disadvantages of using the spectrumanalysis capabilities of an oscilloscope
or other multifunction instrument vs. a
dedicated signal or spectrum analyzer?
Belleau, Anritsu: "Digital oscilloscopes
fundamentally measure signals in the
time domain. This limits their upper frequency measurement capability, since
higher frequency measurements require
higher direct measurement bandwidth
and higher bandwidth analog-to-digital
converters (ADC). As ADC bandwidths
increase, the number of bits (ADC resolution) typically decreases, so dynamic
range is reduced. Higher direct measurement BW also goes hand-in-hand with
higher noise, which also limits dynamic
range. Higher bandwidth oscilloscopes
are also significantly more expensive.
Also, performing FFT's on wide bandwidth signals requires significant processing power, so updates of the FFT
spectrum are generally slower than what
is available from a dedicated signal or
spectrum analyzer."
Chonko, SIGLENT: "Integrated FFT/
spectrum analyzer functionality on
an oscilloscope definitely increases its
usefulness. Simply having access to frequency domain data can be useful when
analyzing EMI, modulated signal analysis, and tracking harmonic signal content.
Unfortunately, oscilloscope front ends are
not as sensitive, nor do they provide the
same dynamic measurement range as
a standalone spectrum analyzer. Filter
characterization, VSWR, and full electromagnetic compliance troubleshooting
require the large dynamic measurement
range that is based on traditional spectrum analyzer designs."
Sanchez and Nilsson, Rohde & Schwarz:
"Both products are aiming at different
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