5/1/2015
Agenda
I Anatomy of a Pulse
I
I
Electromagnetic Interference Testing (EMI) Basics - Part 1
Capturing Pulsed / Intermittent Signals with Frequency
Swept, Frequency Stepped, and Time Domain Scan
Methodologies
I Architectures / Methodology
I
I
Photo
Goes
Here
Real World Signals
Spectrum
I
Bill Wangard
I
Bill Wangard is the EMI Receiver and Radio monitoring Product
Manager at Rohde & Schwarz. He has 20+ years of RF and
Receiver experience at Motorola and Rohde & Schwarz. Bill
authored numerous patents at Motorola.
Frequency Swept
Frequency Stepped
Time Domain Scan
Measurement / Dwell Time
I Comparison Videos
I
Frequency Swept vs Frequency Stepped vs Time Domain Scan
Anatomy of a Pulse
Anatomy of a Pulse
Pulse Spectrum
Real World Signals → Real World Problems
I Examples in real world
I Switched Mode Power Supplies
I Radar systems
I Serial data emissions
I Valve opening / closing
I Systematic arching (brush motor at constant RPM)
I Short duration events with heating considerations
Ʈ – pulse width
T - PRI
frequency
Anatomy of a Pulse
Anatomy of a Pulse
Pulsed / Intermittent Signals
Frequency and Time Domain
Pulsed Emissions
I
Minimum dwell time at each frequency in order to catch a pulse
I Related to pulse repetition rate
I If pulse occurs once every 10 ms…
I Then
I
We must dwell for
I
10 ms at each
eque cy …
I
frequency
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5/1/2015
Agenda
Basic Architectures
RBW
Sweep time
I Anatomy of a Pulse
I
I
Real World Signals
Spectrum
I Swept Analyzer
I Architectures / Methodology
I
I
I
I
Frequency Swept
Frequency Stepped
Time Domain Scan
Measurement / Dwell Time
I Signal Analyzer - aka
I
I
I Comparison Videos
I
Frequency Swept vs Frequency Stepped vs Time Domain Scan
Modern EMI Receiver Architecture
RF
Wideband IF
I
I
FFT Analyzer
Vector Signal Analyzer
Time-Domain Analyzer
Real-time Analyzer
IF BW
Processing
Architectures
Spectrum Analyzer vs. EMI Receiver
Digital Data
I Local
Oscillator
I Detector
DSP
A
D
Digital RBW Filter
Digital Detectors
y
Local
Oscillator
x
Local Oscillator - Sweeping vs. Scanning
I
I Pre-Amp &
Pre-selection
Methodology
Architetures
I
I IF Filter
Controls the measurement frequency
Spend enough time at each frequency to detect pulsed emissions
Frequency Swept (Spectrum Analyzer)
I
I
I
y
x
Continuously swept across frequency range
What is measurement time at each frequency?
I
Time = Sweep Time / Sweep Points
What is the Spacing/Step size between measurements?
I
Step = Frequency Span / (Sweep Points -1)
Example:
- 801 pts over 200M - 1GHz
- 1 MHz per point
- Sweep rate constant across span
- Reduced frequency resolution
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5/1/2015
Methodology
Methodology
Frequency Stepped (EMI Receiver)
Time Domain Scan
Tuned (stop) at each point
Directly set the measurement time (dwell time)
Directly set the frequency step size
I
The Discrete Fourier Transform (DFT) is a numerical mathematical method
that calculates the spectrum for a periodic signal
I
Use DFT to simultaneously measure many frequencies in parallel
Example:
- 4M pts over sweep range (frequency resolution)
- RBW overlap to reduce frequency related amplitude
errors or picket fences
- Dwell time per frequency
- Automatic Gain Control (AGC)
I
The Fast Fourier Transform (FFT) is an efficient algorithm to compute the
DFT using symmetry and repetition properties
I
FFT is much faster than DFT due to reduced number of multiplications
I
I
I
Methodology
Methodology
Time Domain Scan
Time Domain Scan

Time-domain
Sample the frequency interval with high
sampling rate
Frequency domain
Split the measured frequency range into
consecutive frequency intervals

f
F(s) f(t)

Frequency domain
Merge the spectra of all frequency blocks
Fast-Fourier transformation
Transform the signals from time domain to
frequency domain
Measurement / Dwell Time
Measurement / Dwell Time
Frequency Stepped Scan
Time Domain Scan
Input Signal
I Pulse Modulated
I 12 ms pulse period
Input Signal
I Pulse Modulated
I 12 ms pulse period
Even 10 ms
measurement time
yields a closed trace
Zooming in reveals
gaps in the trace
Closed trace with 12
ms measurement time
Gaps in trace with 10
ms measurement time
Important:
Measurement time ≥
signal period
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5/1/2015
Measurement / Dwell Time
Agenda
Spectrum Analyzer Zero Span Mode
I Anatomy of a Pulse
I
Input Signal
I Pulse Modulated
I 12 ms pulse period
I
Real World Signals
Spectrum
I Architectures / Methodology
I
I
Zero span display in
spectrum analyzer
measures signal period
/ pulse repetition rate
I
I
Frequency Swept
Frequency Stepped
Time Domain Scan
Measurement / Dwell Time
I Comparison Videos
I
Series of Videos
I Videos 1-5:
I Input signal: 10ms pulse period (repetition rate) with 10us pulse duration @ 700MHz
I RBW = 100kHz
Video
#
Time
Duration
Freq Range
Method
Sweep/Dwell Time
1
1:34
30M – 1G
Swept
Auto:
1.3ms
2
2:31
30M – 1G
Swept
Per MIL-STD461:
146sec
3
0 08
0:08
30M – 1G
Ti
Time
D
Domain
i
Per MIL-STD461:
MIL STD461:
15ms
4
4:47
650M – 750M
Swept
Per MIL-STD461:
15sec
5
0:09
650M – 750M
Time Domain
Per MIL-STD461:
15ms
6
4:10
650M – 750M
Swept /
Stepped /
Time Domain
Notes
Frequency Swept
Fast Sweep with Max Hold - (1:34)
I Conditions
I
I
Freq Resolution:
Need to Zoom in
Zoom in Freq:
Aliasing, Missed
Events
I
I
10ms PRI with 10us pulse duration @ 700MHz
Sweep from 30MHz to 1GHz
RBW = 100kHz (6dB MIL-STD 461 filters)
Default Sweep Time = 1.3ms
I MIL-STD
MIL STD 461 sweep ti
time spec iis 145
145.5sec
5
I (1GHz – 30MHz) * 0.15sec/MHz = 145.5sec
I Observations
I
1 sec PRI: Time
Domain is superior
to capture
intermittent signals
Frequency Swept vs Frequency Stepped vs Time Domain Scan
I
Take more than 1 minute to capture
Almost have to know it’s there, can be misleading
Frequency Swept
Frequency Swept (2:31)
Fast Sweep with Max Hold - (1:34)
MIL-STD 461 Spec Sweep Time with Max Hold
I Conditions
I
I
I
I
10ms PRI with 10us pulse duration @ 700MHz
Sweep from 30MHz to 1GHz
RBW = 100kHz (6dB MIL-STD 461 filters)
Spec’d
Spec
d Sweep Time = 146sec
I MIL-STD 461 sweep time spec is 145.5sec
I (1GHz – 30MHz) * 0.15sec/MHz = 145.5sec
I Observations
I
I
High probability to capture 10ms PRI pulsed signal, but frequency
resolution is not adequate, must zoom in
Takes 146sec, 2:26
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5/1/2015
Frequency Swept (2:31)
Time Domain (0:08)
MIL-STD-461 Spec Sweep Time with Max Hold
MIL-STD 461 Spec’d Dwell Time
I Conditions
I
I
I
I
10ms PRI with 10us pulse duration @ 700MHz
Sweep from 30MHz to 1GHz
RBW = 100kHz (6dB MIL-STD 461 filters)
Spec’d Dwell Time = 0.015sec = 15ms
I Observations
I
I
Event detected and captured in just a few seconds
Time Domain is much faster and less likely to miss intermittent event
Time Domain (0:08)
Frequency Swept (4:47)
MIL-STD 461 Spec’d Dwell Time
MIL-STD 461 Spec’d Sweep Time
I Conditions
I
I
I
I
10ms PRI with 10us pulse duration @ 700MHz
Sweep from 650MHz to 750MHz
RBW = 100kHz (6dB MIL-STD 461 filters)
MIL-STD 461 sweep time spec is 15sec
I 100MHz * 0.15sec/MHz
I Observations
I
I
I
Frequency Swept (4:47)
MIL-STD 461 Spec’d Sweep Time
Many sweeps are required to properly capture the signal
Takes nearly 3min despite 15sec sweep time
User must be aware of time aliasing if sweep time is an
integer number of the PRI
Time Domain Scan (0:09)
MIL-STD 461 Spec’d Dwell Time
I Conditions
I
I
I
I
10ms PRI with 10us pulse duration @ 700MHz
Sweep from 650MHz to 750MHz
RBW = 100kHz (6dB MIL-STD 461 filters)
MIL-STD 461 dwell time of 15ms
I Observations
I
Peak found within seconds
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5/1/2015
Time Domain Scan (0:09)
MIL-STD 461 Spec’d Dwell Time
Freq Swept vs Freq Stepped vs Time Domain
Capture Pulsed Event (4:10)
I Conditions
I
I
I
I
1s PRI with 10us pulse duration @ 700MHz
Sweep from 650MHz to 750Hz
RBW = 100kHz (6dB MIL-STD 461 filters)
Frequency Swept: Adjust Sweep Time from 1s to 20s
I Observations
Ob
ti
I
I
I
Frequency Swept
I Takes a very long time
I Aliasing is prevalent, especially when ST = 10s and 20s
Frequency Stepped
I Video shows just enough to demonstrate will take a long time
Time Domain Scan
I Peak found within seconds with no issue of time aliasing
Freq Swept vs Freq Stepped vs Time Domain
Summary
Capture Pulsed Event (4:10)
I Pulsed / Intermittent signals are prevalent throughout industry
and must be properly detected / characterized
I Advances in DSP technology enabled new methodology of
Time Domain Scan
I Also enhanced EMI Diagnostic capability, see Part 2
I Traditional Spectrum Analyzer Frequency Swept methodology
has limitations that must be understood to yield proper results
Sweep Time
I # of Points
I Frequency Resolution
I
I Time Domain Scan is very powerful methodology for detecting
and characterizing Pulsed / Intermittent Signals
Thanks for attending!
Don’t miss our Test Bootcamp!
November 12, 2015
www.emclive2015.com
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