Agilent Technologies Agile or Elusive Signals Using Manual

© 2013 Agilent Technologies
Aerospace & Defense Symposium
Analyze Agile or Elusive
Signals Using Real-time
Measurement and Triggering

© 2013 Agilent Technologies
Aerospace & Defense Symposium
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Aerospace & Defense Symposium
This Presentation
Agile & Elusive Signals
Discovering Signals vs. Troubleshooting, Optimizing
Case Studies
Dynamic signal environment-ISM band
Radar signal
Choosing & Using Techniques & Tools
Make the most of what you already know & own
Swept spectrum analyzers
Vector signal analyzers/VSA software
Oscilloscopes
Real time analyzers
Using Triggering to Enhance Measurement Effectiveness

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Aerospace & Defense Symposium
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Case Study #1: 2.45 GHz ISM Band
100 MHz Wide
Spread Spectrum Techniques
Lightly Regulated, Signals Not Explicitly Coordinated
WLAN (typically dominant occupant), Bluetooth, Cordless Phones
•And 1 kW+ microwave ovens!
•And almost anything else!
Very Dynamic
•Content not known at any specific point in time
•Often very low occupancy
Lots of Collision Tolerance Needed
Potential “Cliff Effect” at Some Degree of Crowding

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Aerospace & Defense Symposium
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ISM Band View: Swept Spectrum Analysis
Band: 100 MHz
Span: 160 MHz
Dynamics X2 (swept RBW & changing signals) Confuse the View
Peak Hold Detects Signals but Frequency Overlap Obscures
Signals Typically Short Duty Cycle, Total Low Occupancy
POI is Approximately “Low” (useful concept even if not strictly
applicable)
Single Sweep
(fast but retrace not as fast)
Peak Hold (short)
Peak Hold (long)

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Aerospace & Defense Symposium
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ISM Band View: Real Time Analyzer
Density or
Histogram Display
Gap-Free Analysis
No Signals Missed
Density Display Shows Signals Inside Signals
Fast, Full Display Update Rate Shows Signal Dynamics
See Unexpected Behavior, Even If Infrequent
Individual Display Updates Combine Thousands of Spectra

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Aerospace & Defense Symposium
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Aerospace & Defense Symposium
ISM Band View: Real Time Analyzer
Spectrogram Display
Top Trace is Latest or
Selected Spectrum
Same Spectral Data as
Density/Histogram
Individual Spectrogram Line
Represents Many Spectra
(typically thousands)
View into Dynamics, Timing
Acquisition Time Setting Affects Way Spectra are Combined to Form
Display Update
WLAN Signals Active Continuously?
What are Vertical Bars? A Multitone Signal?

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Aerospace & Defense Symposium
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Spectrogram Display
Adjusting Acquisition Time
Shorter Acquisition Time
Determines Amount of Data
Processed for Spectrum or
Spectrogram Trace Update
Each Trace Update &
Spectrogram Line Represents
Fewer Spectra
More Trace Updates/Second, Finer Time Resolution
Spectrogram Covers Shorter Interval
Determines Time Scale of Spectrogram
Use Spectrogram Trace Buffer to Examine Signal Dynamics

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Aerospace & Defense Symposium
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Aerospace & Defense Symposium
Characteristics of the Real Time Analyzer
Density View
Fast Display Updates, High Data Density
Easily Understand Signal or Event Frequency
Find Very Infrequent Events
Find Unexpected Events, Behavior
Limitations
•Combining traces combines behavior from different times
•Limited flexibility (RBW, span combinations)
•Limited frequency span
•Power spectrum only
•Markers only on combined spectrum or density at a point

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Aerospace & Defense Symposium
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Aerospace & Defense Symposium
What is “Real Time” Analysis?
Understanding Real Time Analyzers and Real Time Analysis
General Definition of Real Time
•Measurement operations where all signal samples are used in calculating
measurement results of some kind (usually spectrum)
Real Time Bandwidth (RTBW)
•The widest analysis bandwidth where an analyzer can maintain real time
operation
•Duration of maintaining real time operation is not specified; it may
assumed to be short term or long term or unlimited
Current Usage for Signal Analyzers
•A spectrum or FFT analyzer having a signal processing path where most or
all samples, even at wide bandwidths, are used to create a spectral display
or to trigger signal measurement or acquisition (sometimes both)

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Aerospace & Defense Symposium
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Real Time Operation
In Real Time Operation the Analyzer’s Processing (CALC) is
Fast Enough to Keep Up with All Data Samples
CALC Time Includes FFT or Power Spectrum, Averaging, Display
Updates, etc.
However some data
may still be “lost”

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Aerospace & Defense Symposium
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If Processing is Faster than Sampling, Perform Additional FFTs With
Partially-New Time Records as Samples Come In
Avoid Loss of Data Due to Windowing
Accurate Amplitude Measurements of Short Duration Signals
Overlap Processing
Overlap 0%
Overlap 50% Processor Idle
Window
Function

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What is a Real Time Analyzer?
Specific Analyzer Type vs. Analysis Characteristic
In this context it means several or all of the following things:
•Gap free: no dead time between acquisitions; all sampled data is
processed; process is continuous
•Consistent measurement & display update speed: all hardware
implementation of FFT spectrum generation and not subject to Windows’
task interruptions
•High speed measurements: many thousands of FFT generated spectra
per second, vastly exceeding software FFT speed
•High speed and/or data-dense displays: combine large numbers of
measurements to form responsive, insight-producing displays
•Spectral trigger or frequency mask trigger (FMT)
•Definitions vary, what is real time analysis for you?

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Aerospace & Defense Symposium
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Aerospace & Defense Symposium
Probability of Intercept (POI)
Treated Informally Here
•Finding signals important to you, expected or unexpected
•Reasonable effort and time to discovery
•Signals found can be measured as necessary
• Knowledge of signals may be “perfect” or simply adequate
A More Rigorous Treatment in Paper From Richard Overdorf
• “Understanding Probability of Intercept for Intermittent Signals“
Evaluate These Techniques Against Your Requirements

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Aerospace & Defense Symposium
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Frequency Mask Trigger (FMT)
Trigger Based on
In-Band Power
(scalar) Spectrum
Spectral Mask
Evaluation, High/Low
Limits, Logic
Trigger Generated
from High Speed
FFT Engine
Trigger Timing Resolution: 1/FFT Period
Trigger Not Time-Aligned
Trigger a Single Spectrum Measurement or Time Capture (VSA), etc.

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Aerospace & Defense Symposium
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Vector Signal Analysis: The Logical Extension
and Complement to a Real Time Analyzer
Superheterodyne Downconversion to All-Digital IF
•Adaptable to swept
spectrum analysis and
real time analyzer
•Full vector data
preserved
Capture
Memory
Measurements
•Short/Long Data Block
•Vector, Demodulation

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Aerospace & Defense Symposium
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VSA Spectrum of ISM Band Signals
Initial Measurement
Not Much More
Informative
FFT Avoids Problem
of Moving Analysis
Aperture (RBW filter)

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VSA Spectrum of ISM Band Signals
Long Time Record (100,000 points)
Much More
Informative
Higher POI Spectrum
Magnitude or RF Envelope
Color Persistence Spectrum

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VSA Spectrum of ISM Band Signals
Long Time Record & Enhanced Displays
Not Real Time with
“Live” Measurements
Is Real Time Plus
Overlap with Time
Capture and Playback
Separating History
(frequency of
occurrence) and
“Recency”
Select Segment/Region
to Analyze from Time
Capture buffer
Many Spectra Combined
Digital Persistence
Cumulative History

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Improving POI with FFT Analyzers
Several Steps for Dramatic Improvement
Use Much Longer Time Records (25,000 points or more)
•Time record length goes up faster than FFT speed goes down
Narrow Frequency Span to the Minimum Needed
•Time record is longer (in time) for given number of points
Use IF Magnitude Trigger, Pre/Post Delays, Holdoff
•Avoid measuring when no signal present in span
Use Persistence or Density/History Displays
•Typically persistence, to make peaks last long enough to be noticed
Peak Hold
Result: POI Dramatically Improved, Though may not be Near 100%

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Aerospace & Defense Symposium
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Aerospace & Defense Symposium
Triggering in VSAs and Real Time Analyzers
IF Magnitude & Frequency Mask Triggers
Triggered Individual Measurements or Signal Captures
•Sqrt (I2+ Q2) of each
sample, is easier &
faster (VSAs)
•FFT power Spectrum
is slower but more
selective (RTSAs)
•VSA now does both
Capture
Memory
Measurements
•Short/Long Data Block
•Vector, Demodulation
IF Mag or
Freq Mask Trig