EMI Testing Using Spectrum Analyzers vs. Test Receivers

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
-20
0
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
-20
0
30M 50M 70M 100M 200M 300M 500M 700M 1G
�� 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

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

Level [dBµV]
120
100
80
60
40
20
-20
0
Spectrum Analyzers for EMI
30M 50M 70M 100M 200M 300M 500M 700M 1G
�� 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

Level [dBµV]
120
100
80
60
40
20
-20
0
Spectrum Analyzers for EMI
30M 50M 70M 100M 200M 300M 500M 700M 1G
�� Subrange Issue Revisited
- Per CISPR ½ RBW recommendation
- For unit with 500 point unit = 30 MHz Spans
- Solution: 970 MHz Span = 32 Spans required!

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 SA have 1-3-5 Steps RBW
- EMI Filters ..200 Hz, 9 kHz, 120 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 � 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

120
100
80
60
40
20
0
50.00
40.00
30.00
20.00
10.00
0.00
Test Receivers for EMI
30M 50M 70M 100M 200M 300M 500M 700M 1G
Level [dBµV]
57.00
79.94M 85M 90M 95M 100M 109.63M
Frequency [Hz]

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 use outside EMI, 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?
�� TR is optimum for final
(dwell time &
auto attenuator)
�� Use SA or TR for hit list
Use SA or TR for maximization
Att 30 dB AUTO
RBW 120 kHz
MT 1 s
PREAMP ON
FREQUENCY 931.9200000 MHz
LEVEL QPK dBµV
10 20 30 40 50 60 70 80 90
dBµV 100 MHz
60
50
200 MHz 300 MHz 400 MHz 500 MHz 600 MHz 700 MHz 800 MHz 900 MHz
1 PK
FCC15RB
40
CLRWR 30
20
10
0
-10
-20
30 MHz 1 GHz
Date: 8.SEP.2003 14:13:12
SGL

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

Ref Level
0dB
amplitude
Samples and pixels
detector
peak
QP
Ave
Min Peak
Display Pixel n
samples
amplitude
detector
peak
QP
Ave
Min Peak
Display Pixel n + 1

120
100
80
60
40
20
0
Sample Points Example
30M 50M 70M 100M 200M 300M 500M 700M 1G
Level [dBµV]
57.00
50.00
40.00
30.00
20.00
10.00
0.00
79.94M 85M 90M 95M 100M 109.63M
Frequency [Hz]
�� Example: TR vs. SA sample points

1 SA
AVG
RF Overload Example
MARKER 1
RBW 3 MHz
496 MHz
VBW 10 MHz
Ref 0 dBm 1 * Att 10 dB SWT 10 ms
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
Center 1 GHz
Date: 23.JUN.2004 20:33:37
200 MHz/
�� Example: amplified signal at 500 MHz
2
Marker 1 [T1 ]
3.03 dBm
496.000000000 MHz
Marker 2 [T1 ]
-48.80 dBm
996.000000000 MHz
Marker 3 [T1 ]
-48.60 dBm
1.500000000 GHz
3
Span 2 GHz
A

OVLD
1 AP
CLRWR
IF Overload Example
RF ATTENUATION
RBW 3 MHz
10 dB
VBW 10 MHz
Ref 0 dBm
* Att 10 dB 1 SWT 5 ms
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
Center 502.0534106 MHz
Date: 23.JUN.2004 20:55:20
99.02160153 MHz/
�� Example: +6 dBm Pulse
Marker 1 [T1 ]
6.13 dBm
502.053410569 MHz
Span 990.2160153 MHz
A

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

1 PK *
CLRWR
Overdrive and Preselection
MARKER START FREQUENCY 1
RBW 3 MHz
1.000272533 600 MHz GHz
VBW 10 MHz
Ref 0 dBm
* Att 20 dB SWT 10 ms
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
Start 400 600 MHz 141.6135906 121.6135906 MHz/ Stop 1.816135906 GHz
Date: Date: 8.SEP.2003 8.SEP.2003 13:04:47
13:03:46 13:04:13
1
1
�� Example: +10 dBm signal at 500 MHz
1
Marker 1 [T1 ]
-43.41 -62.14 dBm
1.000272533 GHz
Marker 2 [T1 ]
-54.36 -54.58 -63.57 dBm
1.501204189 GHz
2
2
2
A
PS

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)

1 RM AV QP *
CLRWR
Detector Settings Example
Ref -20 dBm Att 10 dB
-20
-30
-40
-50
-50
-60
-60
-70
-70
-80
-80
-90
-90
-100
-100
-110
-110
RBW RBW 120 120 kHz kHz
VBW 1 MHz
SWT 175 ms
-120
-120
Start 0 Hz 50 MHz/
Stop 500 MHz
Start 0 Hz 50 MHz/
Stop 500 MHz
Date: 23.JUN.2004 21:44:41 21:45:04
Date: 23.JUN.2004 21:44:15
�� Example: -40 dBm signal at 280 MHz
1
1
1
Marker Marker 1 1 [T1 [T1 ] ]
-49.64 -56.89 -76.57 dBm
280.000000000 MHz
A

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 IF -> If overload flag
Attenuator Ref Level
�� Preamps
amplify at antenna know linear region below 1gz
system check (attenuator) static

Conclusion
�� Go Yankees… Enjoy the Game!
Vic Hudson
Rohde&Schwarz
EMC Systems
Ph 847 612-0618
Vic.Hudson@rohde-schwarz.com