Application Note
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
RF Signal Monitoring and Spectrum Management applications have special equipment
requirements that often go well beyond the typical radio receiver or spectrum analyzer.
The Real-Time Spectrum Analyzer (RTSA) has many superior capabilities for signal
monitoring and spectrum management applications.
In this application note we will focus on how the performance and features of the Tektronix
RSA6100A Series instruments are changing the way advanced spectrum management
is accomplished. We will particularly examine applications for the two newest RTSA
technology advancements - Live DPX™ displays and the very wide 110 MHz Real-Time
triggering and capture.
Covering frequencies through 14 GHz, the RSA6100A leads the industry with up to 110 MHz
of instantaneous IF bandwidth simultaneous with a minimum of 73 dB of dynamic range.
Combining this raw hardware performance with innovative features like live DPX™ displays,
makes the RSA6100A an excellent choice for advanced monitoring needs.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
RSA6114A Real-Time Spectrum Analyzer
(Simplified Block Diagram)
Figure 1. The simplified block diagram of the RSA6114A Real-Time Spectrum Analyzer with Digital Phosphor technology (DPXTM) illustrates the
real-time architecture.
Introduction
In recent years, the explosive growth of wireless devices
and RF communications has created a significant challenge
for the regulatory and interference hunting communities.
In this application note we will see how RTSA technology
can be used to gather key decision making information
from today’s challenging spectral environment.
To see how the RTSA can effectively capture the information needed, we’ll begin with a short review of the RTSA
technology. We will then have a more in-depth overview
of the new technology developed for the revolutionary
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DPX™ display followed by a look at its application to
signal monitoring.
Next, we will examine the technical challenges of signal
identification in wide spectrum bands in light of the
110 MHz capture bandwidth of the RTSA.
Several examples of Spectrum Monitoring applications
will be presented.
Finally, both Analog and Digital IF outputs provide for
external demodulation or recording, and some special
features for protecting results will be presented.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
The RSA6100A’s Performance
The RSA6100A Real-Time Spectrum Analyzer offers
solutions to historically difficult spectrum management
and monitoring problems, expanding the measurement
envelope in bandwidth, frequency, dynamic range and
display processing for a single instrument. Let’s examine
the RSA6100A’s unique capabilities.
Conventional Spectrum
Analyzer Display
RSA6100A DPXTM
Spectral Display
Nearby Laptop
Maximum Trace
Access Point
Frequency Range
The signal path of the RSA6114A begins with an analog
RF down-converter. Using multiple conversions, the RF
section is similar to many spectrum analyzers with the
notable exception of its wide IF bandwidth.
The down-converter tunes over a frequency range from
9 kHz to 14 GHz, covering well beyond most of the popular
communication bands.
Figure 2. A live DPXTM spectrum easily reveals detail like multiple
overlapping WLAN signals. Conventional spectrum analyzers can
only show the peak amplitude in a monochrome trace. This is the
same signal in both halves of this photo.
Wide Bandwidth
The RSA6100A combines a 40 MHz (standard) or 110 MHz
(Option 110) capture bandwidth with high dynamic range.
This bandwidth requires a change in the RF portion of
the instrument architecture from conventional spectrum
analyzers. Previous instruments have used narrow tunable
filters as pre-selectors for image and spurious control.
These filters have significant tuning hysteresis and passband variability, making it difficult to achieve repeatable
results over multiple measurements. When wide-band
captures are needed, conventional instruments require
that the YIG filter be bypassed, with a resultant reduction
in spurious-free dynamic range. For these reasons, the
RSA6100As use a series of switched band-pass filters
for image and spurious control above 8 GHz, achieving
both high spurious-free dynamic range and wide bandwidth
simultaneously.
The DPX™ Display
A unique capability of the RSA6100A that is of particular
interest in Spectrum Management is the live DPX™
spectrum display. The DPX™ system can process more
than 48,000 spectrum measurements per second,
assuring reliable discovery of short duration events.
The signal discovery advantages of DPX™ display technology are particularly useful in spotting the unexpected
transient anomaly, or finding signals hidden under other
signal spectra.
A comparison of the spectrum analysis display of both a
traditional analyzer and the DPX™ spectrum view helps
to illustrate the difference between the two instruments.
In Figure 2, a composite view of the two displays is shown.
The DPX™ display is color-graded, such that infrequent
events are shown in blue, and more frequent events
(such as the noise floor) are seen in red. The swept
analyzer is able to capture the tallest signal in max-hold,
but not the weaker signal. It is also unable to indicate
how often it occurs.
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3
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
RF
Transform Sample Sets
DFT Spectrums
Pixel Histogram
Temp. Grading
9 kHz - 14 GHz
100 Msps or 300 Msps (Opt. 110)
48,828 DFT/s
1464 DFT/Frame
33 Frame/s
Analog RF
to Digital
Conversion
Discrete
Frequency
Transform
1
1
2
5
Pixel
Buffer
Memory
2
1 6
7
9 9 9
Display
Color
Grading
2
7 1
8
9 9 9
Real-Time Spectrum Analysis
(DFT Computation is Completed Before Next Sample Set)
Figure 3. The DPXTM Engine starts with the digital output of the Analog-to-Digital converter. It converts to the Frequency Domain, and compresses
the results into a visable display.
The Technology of the DPX™ Transform
Engine
The RSA6100A’s real-time spectral processing along with
the DPX™ transform engine can be seen in Figure 3.
The analog RF input signal is down-converted and sampled
into transform sample sets. Each sample set is then
transformed into the frequency domain with the Discrete
Frequency Transform (DFT). The frequency transform is fast
enough that transient signals as short as 24 microseconds
will produce a full amplitude DPX™ display.
The DFT spectrums are sent to the DPX™ pixel memory
buffer where a histogram of pixel occurrence is accumulated. After each frame is accumulated, the occurrence rate
is then color coded and output to the display.
The DPX™ spectrum processing rate is much faster than
the human eye can perceive, or that a display can show.
To view live signals it must be slowed down without losing
information. The DPX™ display processor compresses
the measurements to approximately 33 screen updates
per second. The energy found in each pixel location of
the display is accumulated over the hundreds of spectrum
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measurements taken during each display frame. The color
of each pixel in the display is based on the number of
times that energy is found at each pixel location during a
display frame.
Adjustable, phosphor-like persistence of each display frame
then allows short events to remain on the display long
enough to be seen by the human eye. More information on
this revolutionary technology can be found in other DPX™
spectrum display application notes available from Tektronix.
DPX™ and the Crowded Spectrum
These are examples of some dramatically varying signals,
and multiple signals that are sharing the same spectrum.
Without the ability to view them all, we may not know if
they are time-sharing effectively, or if they are interfering
terribly with each other.
DPX™ can help you see varying RF previously impossible
to separate or even to see at all.
You can now reliably view elusive RF signals that ordinary
digital displays cannot show in a crowded spectral
environment.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 4. Many signals are simultaneously visible in the 2.4 GHz
band. Three WLAN channels, a Bluetooth set of signals, and in the
background can be seen several very wideband infrequent signals.
Multiple signals simultaneously
When multiple signals are present in a single spectrum
segment, and when they overlap, traditional analyzers
have little ability to allow viewing these signals as separate.
The digital display usually simply shows the strongest signal
at each frequency point of the spectrum.
Figure 5. Here we see a WLAN base station (The red hump in the
noise). It is the weakest signal seen here, as it is furthest away. In
this color scheme, the red signifies that transmissions are nearly
continuous. The same channel has the nearby laptop computer
which is the strongest signal. However, it is blue as its transmissions
are very infrequent. The four channels with four carriers each are
all part of a Bluetooth signal.
Time-Sharing signal types
In Figure 4 there are three channels of WLAN as well as
a Bluetooth transmission, along with several low-repetition
very wide-band signals that cover the whole band.
One display can separate and reveal several attributes of
time-varying signals even when they completely overlap.
Amplitude and frequency-of-occurrence can clearly be
separated and viewed. The total percentage of time that
a signal is present is displayed as color.
When many signals as diverse as these are all present, it
is difficult to see which ones are present at the same time,
at different times, or even to separate out the different
signals at all.
Amplitudes and frequencies of signals are displayed
using the traditional spectrum analyzer axis. The DPX™
display has variable persistence as well, which increases
the visibility of short pulsed signals.
When two time-varying signals are overlapping, the DPX™
display can easily show them as distinct. Note in Figure 4
how multiple overlapping WLAN signals even on the same
channel are easily distinguished. And the color of the
signals tells us how frequent or infrequent each part of
the signal may be.
Time-Varying Signals
The wideband noise-like infrequent signals can be easily
seen to interfere with all of the other signals at once, and
it is easy to see which of the intended signals are stronger
than the interference, and which are weaker.
Some signals by their very nature have large spectrum
variations over time. One such signal is Analog Television.
While the main carrier and the sound carrier are relatively
constant, the modulation products due to the video
information are constantly changing as the picture changes.
A picture with lots of detail, a picture with lots of color,
and a picture of a large solid subject will have dramatically
different spectral components.
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5
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 6. Analog Television transimissions have continuously
changing spectrum components due to the constantly changing
pictures being trasmitted.
Figure 7. Digital Television transmissions have much more stable
spectrums than analog ones. Note the three communications
signals just above this TV station.
When measuring an analog TV signal for spectrum compliance, the DPX™ allows seeing both the average occupancy
and the nature and extent of the spectral extremes.
Digital TV transmissions are much more time-stable than
analog ones. Figure 7 shows a DPX view of an 8-VSB
US DTV signal.
In Figure 6 we see one analog television transmission. A
traditional digital display would either have each update
show one solid color that encompasses all of the spectral
energy since the last update, or a stored display that
shows a solid color for all spectral energy since the
storage was reset.
Spectrum monitoring is still critical for digital TV, due to the
fact that the digital signal more completely fills the available
assigned bandwidth. Any small failure to conform to the
assigned mask will spill heavily into adjacent channels.
Note that just above this Channel 4 DTV signal are several
72 MHz communications signals. They must be protected
from interference from the DTV broadcaster.
The DPX™ display shows the rate of occurrence of each
of the spectral components graded from “Often” (red) to
“Rare” (blue).
Here we see the constant carriers in red and a complete
view of all of the video picture spectra as they are varying
from each line and frame to the next.
On the low-frequency side the “Vestigial Sideband” is clearly
seen. Note the blue areas that show spectrum components
that recur only occasionally. It is these components that
have a great risk of violating the spectral emissions requirements and will easily be missed with traditional spectrum
analyzers.
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While the filtering on DTV transmitters is usually very good,
it still bears monitoring occasionally.
110 MHz Capture Bandwidth
Wide Bandwidth and Dynamic Range
together
One important attribute of monitoring equipment is sufficient
dynamic range and selectivity to avoid jamming from
large signals closely located to the desired frequency.
Equally importantly, a large bandwidth allows capture of
entire communications bands in one acquisition.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Weak Signal
with marker
Figure 8. Two very large signals. The markers show where the
analyzer’s intermodulation products would be if they were visible.
Figure 9. A weak signal 74 dB below a powerful signal and only
1 MHz away is away is very visible in a 100 MHz span.
The unlicensed 5 GHz U-NII band is fully 100 MHz wide
and the 2.4 GHz band is 83.5 MHz wide. These wide
bands can be captured completely and continuously with
the RSA6100A.
In Figure 9, we are using an analysis bandwidth of 20 kHz,
and can very clearly see a target signal only 1 MHz away
from the large signal while it is 74 dB weaker than the
large signal.
Strong interferers or adjacent signals within the band of
interest can create intermodulation products in the analyzer
that prevent successful demodulation of the desired signal.
Unwanted intermodulation products also tend to clutter
up the spectrum with meaningless signals that slow the
spectrum survey process.
This combination of performance plus a 110 MHz analysis
bandwidth allows the RSA6114A to capture RF signals
with excellent sensitivity under difficult spectral situations.
In Figure 8 we see two large signals in a Spectrum View
that is 100 MHz wide, demonstrating the dynamic range.
Bandwidth and Sensitivity together
A typical Displayed Average Noise Level (DANL) of -151
dBm/Hz helps ensure that low-level signals are detected.
When using the Internal Preamp, the RSA6100A has a
typical DANL of -166 dBm/Hz, further improving sensitivity.
The RSA6100A Series has 73 dB of spurious-free dynamic
range at the full 110 MHz bandwidth, which enables the
analyzer to handle a wide variety of monitoring applications.
Monitoring Applications
Regulating the Spectrum
The radio spectrum is a shared resource with extensive
regulatory requirements designed to avoid unwanted
interference between users. Enforcement groups routinely
monitor emissions to ensure transmission equipment
complies with regulations.
Compliance monitoring is often thought of as solely
a governmental activity. In reality, many commercial
enterprises continuously monitor signals. The growth of
commercial signal monitoring applications has increased
significantly with the explosion of wireless devices,
global news coverage and frequency band auctions.
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7
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 10. A Spectrum Emissions mask can graphically show violations, or an RTSA can trigger on and capture such violations even if they are
infrequent.
Inadvertent interfering emissions can be very costly to
cellular frequency band operators. Likewise, commercial
broadcasters can lose substantial market audiences to a
poorly controlled adjacent channel station. Satellite, teleport
and gateway earth stations need to monitor signals not only
for interference issues, but also for asset usage and billing
purposes. Determining fault in interference cases begins
with monitoring of transmitted spectral emissions.
Spectrum regulators usually need to monitor many different
signal types to determine if enforcement actions are
warranted.
Capturing LPD Transmission Bursts
The RTSA presents a unique solution to reliably capturing
the Low Probability of Detection signal with its real-time
pre-capture analysis, improving the probability of detection
to 100%.
The RTSA’s Frequency Mask Trigger (FMT) can analyze
the input signal for transmission bursts and reliably trigger
on an LPD event. For the RSA6100A Series, the 110 MHz
bandwidth allows 100% probability of capture with signal
durations as short as 10.3 microseconds.
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Bug Hunting
Industrial companies consider their processes and products
to be proprietary. They wish to protect their investment in
these ideas. Sometimes this protection involves hunting
for the possibility that a competitor may have “bugged”
corporate offices with a listening device.
While most listening devices are exceedingly simple, some
are getting more and more sophisticated as communications RF technology has advanced. For example, some
devices may well employ “store-and-forward” digital technology. This mode of operation digitizes the sound and
compresses the digital record. Then either at a pre-determined time, or on command, the device transmits the
digital record as a short burst of modulated RF.
These bursts may be at random times, and finding them
with traditional swept spectrum analyzers can be almost
impossible. The RTSA is exactly the right tool to see and
capture intermittent burst transmissions.
To find this type of intermittent signal, a wideband capture
can be triggered using a Frequency Mask which has
been constructed to avoid the legitimate local RF signals.
Figure 11 shows a spectrum of the FM Broadcast band.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
A Frequency Mask has been constructed to trigger on any
signal that shows up in between the legitimate signals, even
if only lasts for a very short time.
The spectrum has been triggered on a short burst of
digitally modulated signal from such a “Store-and-Forward”
type of bugging listener. This signal is 40 to 50 dB below
the FM signals, even though the RTSA was very much
closer to the digital transmitter than to the FM transmitters
(20 feet compared to 15 miles).
Figure 12 was also generated from this same trigger. It is
a Spectrogram showing the digital signal in between the
FM carriers, and it shows the timing of the burst.
Figure 11. The Frequency Mask with fingers extending down
between the FM signals. The digital burst triggers an acquisition
when it enters the mask.
Another way to see the short bursts is to use the DPX
display mode. Figure 13 is a DPX display of the same spectrum as Figure 11. Here we see the burst differentiated
from the more constant signals by its color. The relatively
constant broadcast signals are red, while the infrequent
burst is a light blue. An active DPX display will also change
dynamically as the burst starts and then fade depending
on the DPX Persistence setting.
Clearing a Frequency Band
As new technologies are developed, and as the spectrum
needs of large populations change, the regulations that
assign frequencies to different users are occasionally
changed. When these assignments change, some of the
users may remain unaware of the reassignment. In some
cases, the reassignment may have been deferred until such
time as the new user is ready to occupy the frequency.
Figure 12. The Spectrogram shows the timing of the digital burst.
In these situations either the government regulators or
sometimes the new users, may need to search and locate
the old users so as to notify them that they need to complete their frequency move.
Very wide-band searches may need to be made to locate
the old signals in an entire frequency band. With the
latest RTSA instantaneous capture bandwidth of 110 MHz,
large bands can be inspected continuously.
Figure 13. The DPXTM showing the infrequent burst as a lighter blue.
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9
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 15. The correct transmitter emission is shown in the left
circle. The spurious oscillation is in the right two circles.
Figure 14. Audio Demodulation of a specific FM radio channel.
Note that the channel can be tuned with a selected marker.
The Receiver BW can be specified up to a 500 KHz BW, and the
demodulaed output played through the instrument’s speaker or
headphones. The channel to be demodulated is selected on the
DPX display and in this example, is also seen on the Spectrogram.
Practical Spectrum Enforcement
The RF spectrum is continually getting more crowded.
Many geographic areas now have more than one cellular
telephone device per person. More consumer devices are
starting to communicate with each other, and computer
networking is expanding at a phenomenal rate.
All of these competing spectrum users must coexist
without serious interference. Even the space between
many RF signals now contains more signals. In such
an RF environment all equipment must meet spurious
emission requirements to allow neighboring signals a
clean path.
And occasionally even in more open environments with
fewer users, a malfunctioning electrical device may well
wreak havoc with licensed users. Enforcement of the rules
is necessary.
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Audio demodulation for analysis and signal
identification
It has been said that the human ear is the fastest detector
for signal recognition. This can be true for both conventional
AM and FM audio signals as well as certain other signals –
a user can become familiar with certain patterns and tones
of a particular signal. Examples could be listening to regular
Citizen’s Band communication, as well as audio from the
FM or AM radio frequencies. Audio signal strength could
also be used to aid in direction finding. The RSA6100A has
the first live signal viewing combined with live signal audio
demodulation.
In Figure 14, we see the setup for this type of analysis.
Here, we are analyzing the FM transmit band. A marker
can be placed over a specific frequency to listen to a
particular channel. Because of the RSA6100A’s dedicated
real-time hardware, demodulation is implemented
concurrent with other analysis.
Taxicab Company Example
One instance of spurious interference was a series of
disruptions to many communications radios operating in
the 450 and 460 MHz bands in a major city. The interference would show up for several minutes at a time, but
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 16. Spectrum and spectrogram showing the interference
sweeping through the satellite signal.
then would be gone for hours at a time. Since the problem
would be gone for most of the day, there were not enough
complaints for anyone to realize that the interference was
affecting an entire communications band.
One user wanted to resolve their problem, and the
Frequency Mask Trigger along with the Spectrogram was
able to find this interference.
As can be seen on the spectrogram in Figure 15, the
interference (the higher frequency signal circled on the left)
exists at times exactly coinciding with one of the legitimate
communication signals (circled on the left side of the
display). The ability to see these timing relationships across
an entire band has allowed identifying the one transmitter
in the city that had a spurious oscillation.
This oscillation can be seen to rapidly change frequency as
it starts up. This was therefore sweeping across several
channels licensed to other users, disrupting them all one
after the other. Then it would settle on a frequency dependent on the temperature at the transmitter site. This is why
the interference changed from time to time.
In this case, the transmitter, owned by a Taxicab company,
had been improperly modified, and when it was replaced
with a new unit the problem was resolved.
Figure 17. Detail time view of the swept signal at its high-frequency
peak.
Emissions from Consumer Products
A particularly difficult spectrum management problem arises
from the proliferation of all manner of consumer products
that utilize RF in one way or another. One case history
started out as interference to the satellite reception of
training videos for EMS responders. The video reception
was interrupted at random times, usually persisting for
hours at a time.
The satellite video provider as well as the reception equipment vendor worked unsuccessfully to resolve the difficulty.
No traditional test equipment could see the problem.
The RTSA was able to trigger on the interfering signal.
Figure 16 is a spectrogram showing the digital satellite
signal (tapped from the IF downlead) with the interfering
signal sweeping through the video transmission. The
interference was present within the desired signal for only
500 microseconds at a time, but this was enough to
cause the receiver to lose signal lock.
The RTSA center frequency was stepped until the ends
of the sweeping signal were found. Figure 17 is the spectrogram of the high frequency end of the sweep. The total
sweep was 260 MHz, and it repeated at apparently random
intervals. Sometimes the sweep was different widths.
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11
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 18. Settings for the user-defined limit line mask. The
user can input specific absolute or relative frequency and power
coordinates to draw the mask.
Now that the signal characteristics were known, the RTSA
was taken mobile to hunt down the source. This proved
initially challenging, as the signal appeared to come from
several directions at once. However, as the monitoring
vehicle followed one particularly strong signal, the culprit
was identified.
The interference emanated from a cheap radar detector
in a parked car. There turned out to be quite a few of
these units in town, and sometimes they were parked
in various locations closer or farther from the receiving
satellite dish.
The fix for this problem was to use a different location for
the receiving dish, hidden behind a building rather than
the original location on a rooftop.
Limit Search and Saving Data on Violations
It can be very useful to continually monitor a specific
section of spectrum to detect violations. This can be
applied when measuring emissions from consumer
products or for other applications. In Figure 18, we
see the RSA6100A series example of a user-defined
search criteria applied to a signal. The search limits could
12 www.tektronix.com/rsa6100a
be a user-defined power level or be drawn according to
specifications such as communication standards and EMI.
The amber area indicates the search violation zone. Once
the signal violates the search zone, it is indicated in red
on the display. There are several useful actions that the
analyzer can take once this violation has occurred, such
reporting by a simple audio indication (beep), saving the
trace information, the displayed screenshot and/or the
acquisition data.
In some cases, it is desirable to have the instrument save
every acquisition that causes a trigger event, whether it be
an external trigger, a frequency mask trigger, a level trigger,
or a user-forced acquisition. This is easily accomplished
by setting the search criteria so that it is always violated by
any acquisition. This results in a “save on trigger” condition,
meaning every acquisition will be saved for later analysis.
This can be particularly useful as this allows real-time signal
monitoring, enabling 100% Probability of Intercept for
signals lasting as short as 10.3 µsec. Once a signal breaks
the Frequency MaskTrigger and Limit line, it would be
saved if the “Autosave Acquisition Data” option is selected
in the limit line area.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 19. Actions that can be taken on a mask violation, such as
saving the data as a trace, picture, or the IQ acquisition data itself.
Note that when the mask is drawn the same as the Frequency
Mask Trigger mask, the RSA6100A can be used to save the data
on a trigger.
Figure 20. Setup of correction tables on the RSA6100A.
Gain/Loss Correction Tables
When integrating any analyzer into a Spectrum
Management system, it can be useful to enter gain and
loss correction factors to account for external equipment
such as antennas, transducers, and preamps that may be
used in a system. The RSA6100A has the ability to enter
these tables and settings can be saved for different
configurations. There is no limit to the number of tables that
can be created – these are all Windows files, so they can
be created and edited off line. Figure 20 shows an example
of setting up a correction table on the RSA6100A.
SDR Verification
Software Defined Radio presents an entirely new generation
of problems. Many burst-type of cellular radios have what
is sometimes called “Spectrum due to Switching transients”
specification due to the burst turn-on and turn-off times.
This can create wideband interference.
SDR takes this problem one step more advanced, as the
radio may well switch between several different modulation
formats during operation. The wideband nature of such
switching of the RF may spread over an entire communications band. The RTSA can not only show the spectrum,
but also the time-domain display of the RF as it changes.
One special branch of SDR is Cognitive Radio. This is
a radio that can listen to the local RF environment and
determine if some spectrum is currently unused. It will
also look up the local government rules to see if it is
allowed to use the spectrum. There are new regulations
now for these radios, requiring a very short time for the
radio to vacate some channels when the primary licensee
starts transmitting.
The RTSA is uniquely capable of measuring this “signal
avoidance” time by setting up a Frequency Mask trigger
and capturing the time-domain nature of the cognitive
radio as it switches to a new frequency.
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Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 21. Crowded VHF and cellular tower, and crowded
mircrowaves too.
Radar System Interference
Many civilian radar systems (such as found at airports,
ships, and weather stations) may also experience interference, particularly from each other. The RSA6100A Series
has both the frequency range (up to 14 GHz) and the
narrow pulse detection capabilities required to measure
these interferences.
The pulse measurement suite available on the RSA6100A
Series can help an airport maintenance department sort
out interference from amongst the many types of radars
present at the airport itself (Ground control, traffic control,
weather, etc). But if the airport is located near a ship harbor,
the cross-interference may be even more interesting.
Crowded Band Intermodulation
The overcrowding of the radio spectrum has been accompanied by a concurrent overcrowding of the physical
locations where transmitters are installed. Exacerbating
this problem has been a tendency for local zoning regula-
14 www.tektronix.com/rsa6100a
Figure 22. Interference from a rusty roof.
tions to force more RF transmission equipment to share
common facilities.
Figure 21 is a small example of this trend. One technical
difficulty often found at such sites is the mixing or intermodulating of two or more of the signals that are in close
proximity. One or more signals may enter the antenna and
nonlinear amplifier of an unrelated transmitter, causing
multiple unwanted signals to be generated and re-radiated.
This is usually easily fixed by the addition of filters and ferrite
isolators in the offending transmitter’s antenna connection.
However, a much more difficult problem to solve is the
non-linear mixing that results from a rusty roof panel on
a nearby building, or even a rusty bolt in the tower itself.
As in Figure 22, there may be several signals that mix
together to cause the emission problems and the RTSA
spectrogram and Frequency Mask Trigger may be required
to examine the signals for many hours before triggering
and then measuring the time relationships of the various
signals that are being mixed together.
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
The RSA6100A Series is ideally suited for a situation such
as this, because the many co-located signals and the
potential myriad of intermods may easily occupy nearly
100 MHz of spectrum. The dynamic range of the measurement instrument must itself not contribute its own
intermodulation that would mask the offending emissions.
Digital Sample Data Output
Outputs for External Processing or
Recording
There are two forms of signal output from the RSA6100A Analog IF, and Digitized time samples of the incoming RF
waveform.
There are two ways to access the digital data samples:
as acquisition files; or as streaming direct hardware access
to the digital data. All of these outputs can provide the full
110 MHz bandwidth of the instrument.
RSA6114A I-Q File Export Modes
Ethernet, USB, or the CD/DVD can deliver the calibrated,
corrected data files (internal “tiq” format) stored in the
analyzer. ASCII is also available from the RSA6100A Series
to allow generic software to process an acquired signal.
File record lengths are limited only by the available RTSA
memory. Table 1 shows the time resolution and total
available record storage time available for the RSA6100A
Series files.
Span
Time Resolution
Max. Record Length
110 MHz
6.7 ns
1.7 seconds
40 MHz
20 ns
5.12 seconds
5 MHz
160 ns
41 seconds
1 MHz
640 ns
8.19 seconds
100 kHz
5.12 µs
10.9 minutes
20 kHz
20.48 µs
43.7 minutes
Table 1. The time resolution and capture length available for various
capture Bandwidths. The Span controls the Capture Bandwidth.
Direct Digital Output for Continuous
Analysis
What does one do if the signal modulation of interest is
continuous and exceeds the memory capacity? While
file export is limited to the size of the internal acquisition
memory, the Tektronix RSA6100 Series (like its predecessor) has a high-speed Low Voltage Differential Signaling
(LVDS) connection that allows access to the output of the
analog to digital converter. Two values are available for
each sample – In-phase and Quadrature
The RTSA input RF & IF sections convert the selected
signal and pass it to the A/D converter. The digital streaming output provides the digitized time-domain waveform
for external demodulation or other processing.
www.tektronix.com/rsa6100a 15
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Figure 23. The 500 MHz IF Output available on the RSA6100A can be internally filtered to 60 MHz or left at approximately 120 MHz wide.
Real-Time Corrected Data
Analog IF Output Measurements
One outstanding feature of all of the digital I/Q output
methods (file export or streaming data), is that the sample
data is always corrected for both amplitude and phase
variations.
Some monitoring applications may require signal measurements or demodulation functions not available in the
RSA6100A. An external third-party receiver can provide
demodulation or proprietary signal processing
As the signal passed through the RF conversion stages,
the image filters and other components add some amount
of amplitude and phase variations across the acquired
bandwidth. The RSA6100A includes calibrated corrections
in the Real-Time processing of the A/D samples. Unlike
an analog IF output, the digital I/Q data is always corrected
for these variations.
For these circumstances there is an IF output port that is
centered at 500 MHz and designed to work in conjunction
with oscilloscopes and other equipment, such as external
demodulators.
The IF output enables the RSA6100A to serve as a
down-conversion tuner with exceptional performance.
The RSA6100A’s tuning range to 14 GHz, 120 MHz IF
bandwidth, selectable filters and integrated buffer amplifier
greatly simplify the needs for other analysis equipment.
Therefore, an external digital processor will be able to
demodulate or otherwise process and produce highly
accurate data representing the incoming signal. The digital
IF outputs are corrected to the full accuracy of the specifications of the RSA6100A.
16 www.tektronix.com/rsa6100a
The RSA6100A’s IF output is uniquely oscilloscope friendly.
The IF output contains an amplifier circuit that adjusts
the output level to approximately 0 dBm (0.224 volts) for
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
signal levels of -25 dBm at the first mixer of the RTSA.
This eliminates the need for external signal conditioning
amplifiers, reducing setup time, complexity and expense.
The high output level provides a strong signal to the
oscilloscope preventing any loss of dynamic range due
to low IF levels.
RSA6100A Series Removable
Hard Drive Option
The IF output of the RSA6100A, as shown in Figure 23,
is active even while the Real-Time analyzer is making other
measurements. External IF processing or demodulation
can be done while spectral measurements are simultaneously made with the real-time analyzer. This eliminates
the requirement that some traditional swept tuned spectrum
analyzers have for placing the instrument in zero-span
when using the IF output.
For monitoring applications this allows using the spectrum
or DPX function to discover new signals while the IF output
is in use to demodulate one of the signals.
It is important to note that analog IF output measurements
using an external oscilloscope or other equipment can be
different from automated measurements made internally by
the RSA6100A. All digital samples that are provided for
Measurements made with the RTSA measurement routines
have been corrected in amplitude and phase, while the
Analog IF output contains possible amplitude variations and
phase errors that will be seen by the oscilloscope or other
analysis equipment.
Addressing Privacy Concerns
Figure 24. The location of the removable Hard Drive option in the
RSA6100A Series.
often shared between various projects which may wish to
retain their own data.
The RTSA was designed to make mixed operation in
various project areas simple. An optional front-panel
access on the RSA6100A family allows access to the
internal hard drive for quick removal. Taking out the hard
drive and inserting another enables quick removal of all
project data. Inserting a second hard drive then allows
the instrument to work in a completely unrelated project
environment.
Exchanging the Hard Drive
Spectrum Monitoring work may create privacy concerns.
And in the development environment, test equipment is
www.tektronix.com/rsa6100a
17
Advanced Spectrum Management with the
RSA6100A Series Real-Time Spectrum Analyzer
Application Note
Conclusions
Appendix 1: Comparison of RTSAs
Signal monitoring and Spectrum Management applications
have grown more challenging with the exponential growth
of wireless devices and communications links in recent
years.
Many applications can be addressed with more economical
real-time analyzers from Tektronix. The table below outlines
details the differences between the RSA3408A and the
RSA6100A Series as an aid to selecting the performance
level required for your application.
The Real-Time Spectrum Analyzer’s unique architecture
provides DPX™ for unprecedented viewing of transient
signals. And it pre-analyzes the signal to accurately trigger
on and capture transient RF events.
The RSA6114A’s extremely wide bandwidth and high
dynamic range are essential requisites for many monitoring
applications.
Unique RTSA features such as the real-time FMT and
real-time DPX™, as well as removable hard drive and full
bandwidth continuous I-Q data output and export capability
are critical elements for reliable spectrum collection and
information production.
The real-time analyzer’s patented DPX™ and trigger
capability also offer substantial reception advantages
where difficult LPD or LPI signals are encountered.
Models
Specification
Frequency Range
Capture Bandwidth
RSA3408A
RSA6106A/6114A
DC - 8 GHz
9 kHz - 6.2 / 14 GHz
36 MHz
40 MHz / 110 MHz
64 MB / 256 MB
256 MB / 1 GB
Maximum Input (CW)
+30 dBm (1W)
+30 dBm (1W)
Maximum Input (DC)
± 0.2 VDC
± 40 VDC
Capture Memory
Digital I & Q Outputs
16 bits @
16 bits @
50 MSamples/sec. each
150 MSamples/sec. ech
Analog IF Output
standard
optional
IF Output Frequency
421 MHz
500 MHz
IF Analog Bandwidth
IF Filter Shape
System Rise Time
Min. DPXTM Event Duration
36 MHz
120 / 60 MHz
Square Top
Square Top / Guassian
25 ns
25 ns / 10 ns
(DPXTM not available)
24 µs
Table 2. The Tektronix Real-Time Spectrum Analyzers offer a
wide range of performance capabilities to fit the most demanding
monitoring systems and the most modest budgets.
18 www.tektronix.com/rsa6100a
Contact Tektronix:
ASEAN / Australasia (65) 6356 3900
Austria +41 52 675 3777
Balkan, Israel, South Africa and other ISE Countries +41 52 675 3777
Belgium 07 81 60166
Brazil & South America (11) 40669400
Canada 1 (800) 661-5625
Central East Europe, Ukraine and the Baltics +41 52 675 3777
Central Europe & Greece +41 52 675 3777
Denmark +45 80 88 1401
Finland +41 52 675 3777
France +33 (0) 1 69 86 81 81
Germany +49 (221) 94 77 400
Hong Kong (852) 2585-6688
India (91) 80-22275577
Italy +39 (02) 25086 1
Japan 81 (3) 6714-3010
Luxembourg +44 (0) 1344 392400
Mexico, Central America & Caribbean 52 (55) 5424700
Middle East, Asia and North Africa +41 52 675 3777
The Netherlands 090 02 021797
Norway 800 16098
People’s Republic of China 86 (10) 6235 1230
Poland +41 52 675 3777
Portugal 80 08 12370
Republic of Korea 82 (2) 6917-5000
Russia & CIS +7 (495) 7484900
South Africa +27 11 206 8360
Spain (+34) 901 988 054
Sweden 020 08 80371
Switzerland +41 52 675 3777
Taiwan 886 (2) 2722-9622
United Kingdom & Eire +44 (0) 1344 392400
USA 1 (800) 426-2200
For other areas contact Tektronix, Inc. at: 1 (503) 627-7111
Updated 01 June 2007
For Further Information
Tektronix maintains a comprehensive, constantly expanding
collection of application notes, technical briefs and other
resources to help engineers working on the cutting edge of
technology. Please visit www.tektronix.com
Copyright © 2007, Tektronix. All rights reserved. Tektronix products are covered by
U.S. and foreign patents, issued and pending. Information in this publication supersedes that in all previously published material. Specification and price change
privileges reserved. TEKTRONIX and TEK are registered trademarks of Tektronix,
Inc. All other trade names referenced are the service marks, trademarks or registered trademarks of their respective companies.
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