EMI Testing Using Spectrum Analyzers
vs. Test Receivers
Vic Hudson
Rohde&Schwarz
IEEE-LI Presentation
™ Topic of the Meeting Description
⇒ Spectrum Analyzers (SA)
⇒ Test Receivers (TR)
Uses and descriptions of each
™ Reasons for using either or both units
™ Advantages and disadvantages
™ Making accurate measurements
Q&A
™ Who uses what ?
⇒ Spectrum Analyzers (SA)
⇒ Test Receivers (TR)
™ Commercial, MIL-STD or Automotive?
™ Software or front panel ?
™ Novice, Capable, Fluent or Expert ?
Overview
™ EMI Equipment in general
⇒ Spectrum Analyzers (SA)
⇒ Test Receivers (TR)
™ Two Most common tools are SA / TR
Spectrum Analyzers for EMI
Spectrum Analyzers for EMI
Level [dBµV]
120
100
80
60
40
20
0
-20 30M
50M
70M
100M
200M
300M
500M 700M
1G
™ SA Settings for EMI measurements
- Span, Reference Level, RBW, VBW and detector
- Span is the Stop – Start Frequency
- Ref Level is typically the Highest point SA can measure
- Coupling with VBW usually some multiple of the RBW
- RBW usually selected per required standard
Spectrum Analyzers for EMI
™ Reasons for Using SA for EMI
Measurements
⇒ Versatility: Wide range of uses
⇒ Familiarity
⇒ Speed … real or imagined
⇒ Price … real or imagined
Spectrum Analyzers for EMI
Level [dBµV]
120
100
80
60
40
20
0
-20 30M
50M
70M
100M
200M
300M
500M 700M
™ SA setup for EMI Example
- Set Span, RBW and detector
- Span of 970 MHz / 500 points = 2 MHz resolution !
- x samples within RBW are stored
- samples are weighted by some detector
- Common EMI detectors are QP, Ave, Pk, RMS
1G
Spectrum Analyzers for EMI
™ Question
- What was wrong with the previous setup?
™ Answer
- Frequency and amplitude accuracy depend on many
samples falling within each RBW filter width.
- set this parameter with frequency span
Spectrum Analyzers for EMI
Level [dBµV]
120
100
80
60
40
20
0
-20
30M
50M
70M
100M
200M
300M
500M
™ Issue # 1 Subranging Required
- Span of 970 MHz / 500 = 2 MHz resolution
- If using 120 KHz RBW, CISPR recommends
60 KHz sample points (17 x finer than 1 MHz)
- Solution: subrange in the span
700M
1G
Spectrum Analyzers for EMI
Level [dBµV]
120
100
80
60
40
20
0
-20
30M
50M
70M
100M
200M
300M
500M
™ Subrange Issue Revisited
- Per CISPR ½ RBW recommendation
- For unit with 500 point unit = 30 MHz Spans
- Solution: 970 MHz Span = 32 Spans required!
700M
1G
Spectrum Analyzers for EMI
™ Frequency Accuracy of SA
- SA resolution is far too course for EMI
without subranging the CISPR span
- SA frequency accuracy when exploring peaks
influenced by Span, RBW, VBW, marker accuracy
™ Amplitude Accuracy of SA
-
6 dB (EMI) filters vs. 3 dB
QP and AVE detector times are observed
Data correction for system transducers
EUT specific timing issues are considered
Subranges set properly for sample #
RF and IF stages are not overloaded
Spectrum Analyzers for EMI
™ Issue # 2 Proper QP and Average Detectors
⇒ Is QP / AVE Detector CISPR-16-1 Compliant?
™ Issue # 3 Correct CISPR RBW Filters
- Typical
Typical SA
SA have
have 1-3-5
1-3-5 Steps
Steps RBW
RBW
-- EMI
EMI Filters
Filters ..200
..200 Hz,
Hz, 99 kHz,
kHz, 120
120 kHz
kHz
Spectrum Analyzers for EMI
™ Issue # 4 Dwell Time
- Sweep Time vs. Span
- Max Hold
™ Issue # 5 Lack of Preselection/ Overload Protection
-EMI Can be very high – wide
-Real Signal or not?
-How to protect your measurement/ SA
-Verify RF and IF stages are not overloaded
Spectrum Analyzers for EMI
™
Has to be a better way!
Test Receivers for EMI
Test Receivers for EMI
™ What exactly is a EMI Test Receiver?
- Fixed Tuned receiver versus Swept Tuned
- Built-in Firmware for doing only EMI
Test Receivers for EMI
™ Controls for Recievers
- Frequency Span (start / stop)
- RBW Filter and detector
- DWELL TIME at each measurement point
- FREQUENCY INCRIMENT (step size)
- TR adjusts sample x depending on span
- x is often 16,000 – 100,000+
- Span / x = frequency resolution
Test Receivers for EMI
120
100
80
60
40
20
0
30M
57.00
50M
70M
100M
200M
300M
500M
700M
1G
Level [dBµV]
50.00
40.00
30.00
20.00
10.00
0.00
79.94M
85M
90M
95M
Frequency [Hz]
100M
109.63M
Test Receivers for EMI
™ EMI TR Advantages
- Measurement Points
- Tune and Dwell Time method
- DWELL TIME at each measurement point
- FREQUENCY INCRIMENT (step size)
- TR adjusts sample x depending on span
- EMI Specificity
- Automatic Control – ATT, Preselection, Filters
Test Receivers for EMI
™ Conclusion
⇒ TR incorporates EMI control parameters
- STEP SIZE between measurement points
- DWELL TIME at each measurement point
- # of sample points as necessary for accuracy
™ Time Penalty ?
- Time dependant on detector and EUT, not
measurement speed of instruments
Best Instrument for EMI?
™ Pros and Cons of Each
- SA is faster for initial preview
- SA can also be used for RX and TX measurements
- TR has little
little use
use outside
outside EMI,
EMI, expensive
expensive
unit for one use
- SA subranging negates any speed
advantage over TR for EMI
- SA amplitude accuracy easily skewed by
improper settings and interpretation
Which one to use?
™ Use SA or TR for hit list
Use SA or TR for maximization
Att 30 dB AUTO
FREQUENCY
LEVEL QPK
10
dBµV
20
100 MHz
60
200 MHz
30
300 MHz
RBW
120 kHz
MT
1 s
PREAMP ON
931.9200000 MHz
dBµV
40
400 MHz
50
500 MHz
60
600 MHz
70
700 MHz
800 MHz
80
90
900 MHz
50
FCC15RB
1 PK
CLRWR
SGL
40
30
20
10
™ TR is optimum for final
(dwell time &
auto attenuator)
0
-10
-20
30 MHz
Date:
1 GHz
8.SEP.2003
14:13:12
Making accurate measurements
Overload protection
Detectors for EMI
RBW Filters for EMI
Preamps
Accurate Measurement
™ Background
™ Dynamic Range of SA / TR is ~ 160 dB
™ EMC engineers don’t know what signals
they are looking for initially
™ Accuracy killers
- Overloads
- Incorrect detector settings
- PRF & directivity of EUT emissions
- Transducer correction factors
Samples and pixels
samples
Ref Level
detector
detector
peak
peak
QP
QP
Ave
Min Peak
Display Pixel n
amplitude
amplitude
0dB
Ave
Min Peak
Display Pixel n + 1
Sample Points Example
120
100
80
60
40
20
0
30M
57.00
50M
70M
100M
200M
300M
500M
700M
1G
Level [dBµV]
50.00
40.00
30.00
20.00
10.00
0.00
79.94M
85M
90M
95M
Frequency [Hz]
100M
™ Example: TR vs. SA sample points
109.63M
RF Overload Example
MARKER 1
496 MHz
Ref
0 dBm
1
* Att
RBW 3 MHz
VBW 10 MHz
SWT 10 ms
10 dB
0
Marker 2 [T1 ]
-48.80
996.000000000
Marker 3 [T1 ]
-48.60
1.500000000
-10
1 SA
AVG
Marker 1 [T1 ]
3.03 dBm
496.000000000 MHz
-20
dBm
MHz
dBm
GHz
-30
-40
2
3
-50
-60
-70
-80
-90
-100
Center 1 GHz
Date:
23.JUN.2004
200 MHz/
20:33:37
™ Example: amplified signal at 500 MHz
Span 2 GHz
A
IF Overload Example
RF ATTENUATION
10 dB
Ref
0 dBm
* Att
10 dB
1
RBW 3 MHz
VBW 10 MHz
SWT 5 ms
Marker 1 [T1 ]
6.13 dBm
502.053410569 MHz
0
OVLD
1 AP
CLRWR
A
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
Center 502.0534106 MHz
Date:
23.JUN.2004
99.02160153 MHz/
20:55:20
™ Example: +6 dBm Pulse
Span 990.2160153 MHz
Preselection Filtering
™ Preselector is a “tracking” RF filter
- ALL RF power (noise & signals) go into mixer
- high amplitude signals outside span can
influence amplitude and may be aliased
™ Cure: Suppress signals before RF or IF
- SA may not warn of RF or IF overdrive
- IF overload won’t show on display
- Signals outside display ruin amplitude reading
Overdrive and Preselection
MARKERFREQUENCY
START
1
1.000272533
600
MHz
Ref
0 dBm
GHz
* Att
20
dB
RBW
VBW
SWT
3 MHz
10 MHz
10 ms
Marker
[T1 ]
-43.41
-62.14
1.000272533
Marker
[T1 ]
-54.36
-54.58
-63.57
1.501204189
0
-10
1 PK *
CLRWR
1
dBm
GHz
2
dBm
GHz
A
-20
-30
-40
1
PS
1
-50
2
1
-60
2
2
-70
-80
-90
-100
Start
Date:
400
600
MHz
8.SEP.2003
141.6135906
121.6135906
MHz/
Stop
13:04:47
13:03:46
13:04:13
™ Example: +10 dBm signal at 500 MHz
1.816135906
GHz
PRF and Detectors
™ EUT / Detector dwell time requirements
- Must capture “worst case” emissions of EUT
- Cycle time and pulse repetition frequency
may require extended dwell in each subrange
- Some detectors require extended
dwell settings (ave, QP)
Detector Settings
™ QuasiPeak ????
⇒ QP is an attempt to quantify a signals
Impact on a radio receiver (annoyance)
- Factors: amplitude, frequency, width, PRF
™ Quasipeak restrictions
- Dwell time (per step or subrange) > 600 mS
- PRF issues increase dwell time requirements
Detector Settings
™ Peak Detector
- Peak gives “worst case”
- Safest detector; Fast enough to see signals
even with incorrect RBW or dwell settings
™ Average Detector
- Above 1 GHz for FCC
- dwell for ~ 100 mS
- Watch RBW (1MHz or 120 KHz)
Detector Settings Example
Ref
-20
dBm
Att
10
RBW
VBW
SWT
dB
120 kHz
1 MHz
175 ms
Marker
1
[T1 ]
-56.89
-76.57
-49.64
280.000000000
dBm
MHz
-20
-20
A
A
-30
-30
1
AV
1 QP
RM *
*
CLRWR
CLRWR
-40
-40
1
-50
-50
1
-60
-60
-70
-70
1
-80
-80
-90
-90
-100
-100
-110
-110
-120
-120
Start
Start
Date:
Date:
0
0
Hz
Hz
23.JUN.2004
23.JUN.2004
50
50
MHz/
MHz/
21:45:04
21:44:41
21:44:15
™ Example: -40 dBm signal at 280 MHz
Stop
Stop
500
500
MHz
MHz
Transducers and PRF
™ Transducer correction
- CISPR needed a way to eliminate effects of
chambers, antennas and cable losses
- Standards require normalization of these
effects to compare results to limit line
™ EUT dwell time requirements
- Must capture “worst case” emissions of EUT
- Cycle time and pulse repetition frequency
may require extended dwell in each subrange
Conclusion
™ TR vs. SA
Span
Subranges
step size
resolution
dwell time
overloading
preselection
™ RF & IF Overloads
RF -> Harmonics
Attenuator
™ Preamps
IF -> If overload flag
Ref Level
amplify at antenna
know linear region
system check (attenuator)
static
below 1gz
Conclusion
™ Go Yankees… Enjoy the Game!
Vic Hudson
Rohde&Schwarz
EMC Systems
Ph 847 612-0618
Vic.Hudson@rohde-schwarz.com