EMC Evaluation at Green Bank:
Emissions and Shield Effectiveness
National Radio Astronomy Observatory
Carla Beaudet
Green Bank RFI Group Leader
Emissions Evaluation: Standards
• ITU-R RA.769 specifies (typical) power flux
density (PFD) threshold of detectabilty for RA
receivers.
Does NOT translate to Radiated Power of Device without
specifying a distance
• FCC Class B ≈ CISPR 22 specifies allowable field
strength at a given distance.
Translates to Radiated Power of Device
2
Emissions Evaluation:
Practical Limitations and Policy
Options for not creating self-interference:
• 500km! radius electronic device-free zone!!!!
• Contain ALL electronic equipment on site with large
enclosures, or position facilities behind natural
obstacles.
• Use a practical (compromise) approach, but set
policy and adhere to it!
3
Emissions Evaluation:
Practical Limitations and Policy
Zone 21Policy:
Policy:
• No transmitters!
transmitters except
(except43MHz
site radios)
site
• radios.
Electronics that will be mitigated to
• comply
All Installed
withElectronics
ITU-R RA.769
mustinclude:
comply
with
ITU-R RA.769
• Anything
that cannot be easily
• No powered
electronicofftoys; use of electronics
must
be work-related.
(~50K
• Anything
that radiates
in excess of
visitors/year)
FCC part 15 class B levels.
4
Emissions Evaluation: Assessing Equipment
for Compliance with ITU-R RA.769
Spectrum Analyzer Setup and Measurement Results…
Observed RFI Feature
Measured Frequency ( MHz )
Corresponding Wavelength ( meters )
Measured Peak Power ( dBm )
Spectrum Analyzer Resolution Bandwidth ( MHz )
Measured Half-Power Bandwidth ( MHz )
Signal Characteristics
Measured Power Per Unit Resolution Bandwidth ( dBW/Hz )
1
2
210.13
1.43
-64.00
0.010
0.0100
CW
-134.00
3
270.92
1.11
-71.00
0.010
0.0100
CW
-141.00
Receive (Rx) Antenna
Equipment Under Test
(EUT)
4
154.83
1.94
-66.50
0.010
0.0100
CW
-136.50
924.98
0.32
-67.20
0.010
0.0100
CW
-137.20
Amplifier
Test Setup and Total Radiated Power Per Unit RBW Measured During Test…
Test Antenna Number ( Select 1, 2, 3, or 4 from Equipment Table )
Test Amplifier Number ( Select 1 through 7 from Equipment Table )
Test Antenna Gain ( dBi )
Equivalent Test Antenna Collecting Area ( m*m )
Total Transmission Line Loss ( dB ) (modify if different cables used)
Preamplifier Gain ( dB )
Distance From DUT to Test Antenna ( meters )
Calculated Test Setup Space Loss ( dB )
Total Radiated Power Per Unit RBW Measured During Test ( dBW/Hz )
2
3
3.73
0.38
1.10
53.30
7.00
32.06
-154.14
3
3.73
0.23
1.10
53.30
7.00
34.27
-158.93
2
3
2.00
0.47
0.80
53.30
7.00
31.14
-157.86
2
3
6.06
0.03
4.70
53.30
7.00
42.61
-143.19
Predicted Field Strength at Target Distance…
Anticipated Distance to GBT ( meters )
Calculated Field Strength at Target Distance ( dBW/m*m/Hz )
11
-185.96
11
-190.75
11
-189.68
11
-175.01
3.00
3.00
-244.50
-215.52
2.81E+04
28.98
1.00
-241.00
-209.68
1.08E+05
31.32
20.00
-248.80
-208.02
1.58E+05
38.78
Cable
2
#1
Cable #2
Predicted Impact on GBT Observations…
Predictions for CONTINUUM OBSERVATIONS
Corresponding Target GBT CONTINUUM Bandwidth ( MHz )
Corresponding Target GBT CONTINUUM Limit ( dBW/m*m/Hz )
Calculated Field Strength Per Unit CONTINUUM Bandwidth ( dBW/m*m/Hz )
Calculated Field Strength Per Unit CONTINUUM Bandwidth ( Jy )
Feature Exceeds Target CONTINUUM Limit By… ( dBW/m*m/Hz )
Distance (Dtest-244.50
)
-210.73
Predictions for SPECTRAL LINE OBSERVATIONS
Corresponding Target GBT SPECTRAL LINE Bandwidth ( MHz )
Corresponding Target GBT SPECTRAL LINE Limit ( dBW/m*m/Hz )
Calculated Field Strength Per Unit SPECTRAL LINE Bandwidth ( dBW/m*m/Hz )
Calculated Field Strength Per Unit SPECTRAL LINE Bandwidth ( Jy )
Feature Exceeds Target SPECTRAL LINE Limit By… ( dBW/m*m/Hz )
Cable #3
8.46E+04
33.77
Spectrum Analyzer
2.00
-241.40
-208.97
1.27E+05
32.43
2.00
-241.40
-213.76
4.21E+04
27.64
1.00
-238.80
-209.68
1.08E+05
29.12
8.00
-241.60
-204.04
3.94E+05
37.56
PowerTx(dBm) = Pmeasured(dBm) + Lspace(dB) – Gantenna(dB) – Gamplifier(dB) + Lcables(dB)
5
Emissions Evaluation: Assessing Equipment
for Compliance with ITU-R RA.769
Faraday Cages
Low-Pass Filters
RF Absorber
6
Emissions Evaluation: Assessing Equipment
for Compliance with ITU-R RA.769
Spectrum Analyzer Setup and Measurement Results…
Observed RFI Feature
Measured Frequency ( MHz )
Corresponding Wavelength ( meters )
Measured Peak Power ( dBm )
Spectrum Analyzer Resolution Bandwidth ( MHz )
Measured Half-Power Bandwidth ( MHz )
Signal Characteristics
Measured Power Per Unit Resolution Bandwidth ( dBW/Hz )
1
2
210.13
1.43
-64.00
0.010
0.0100
CW
-134.00
3
270.92
1.11
-71.00
0.010
0.0100
CW
-141.00
Receive (Rx) Antenna
Equipment Under Test
(EUT)
4
154.83
1.94
-66.50
0.010
0.0100
CW
-136.50
924.98
0.32
-67.20
0.010
0.0100
CW
-137.20
Amplifier
Test Setup and Total Radiated Power Per Unit RBW Measured During Test…
Test Antenna Number ( Select 1, 2, 3, or 4 from Equipment Table )
Test Amplifier Number ( Select 1 through 7 from Equipment Table )
Test Antenna Gain ( dBi )
Equivalent Test Antenna Collecting Area ( m*m )
Total Transmission Line Loss ( dB ) (modify if different cables used)
Preamplifier Gain ( dB )
Distance From DUT to Test Antenna ( meters )
Calculated Test Setup Space Loss ( dB )
Total Radiated Power Per Unit RBW Measured During Test ( dBW/Hz )
2
3
3.73
0.38
1.10
53.30
7.00
32.06
-154.14
3
3.73
0.23
1.10
53.30
7.00
34.27
-158.93
2
3
2.00
0.47
0.80
53.30
7.00
31.14
-157.86
2
3
6.06
0.03
4.70
53.30
7.00
42.61
-143.19
Predicted Field Strength at Target Distance…
Anticipated Distance to GBT ( meters )
Calculated Field Strength at Target Distance ( dBW/m*m/Hz )
11
-185.96
11
-190.75
11
-189.68
11
-175.01
3.00
3.00
-244.50
-215.52
2.81E+04
28.98
1.00
-241.00
-209.68
1.08E+05
31.32
20.00
-248.80
-208.02
1.58E+05
38.78
Cable
2
#1
Cable #2
Predicted Impact on GBT Observations…
Predictions for CONTINUUM OBSERVATIONS
Corresponding Target GBT CONTINUUM Bandwidth ( MHz )
Corresponding Target GBT CONTINUUM Limit ( dBW/m*m/Hz )
Calculated Field Strength Per Unit CONTINUUM Bandwidth ( dBW/m*m/Hz )
Calculated Field Strength Per Unit CONTINUUM Bandwidth ( Jy )
Feature Exceeds Target CONTINUUM Limit By… ( dBW/m*m/Hz )
Distance (Dtest-244.50
)
-210.73
Predictions for SPECTRAL LINE OBSERVATIONS
Corresponding Target GBT SPECTRAL LINE Bandwidth ( MHz )
Corresponding Target GBT SPECTRAL LINE Limit ( dBW/m*m/Hz )
Calculated Field Strength Per Unit SPECTRAL LINE Bandwidth ( dBW/m*m/Hz )
Calculated Field Strength Per Unit SPECTRAL LINE Bandwidth ( Jy )
Feature Exceeds Target SPECTRAL LINE Limit By… ( dBW/m*m/Hz )
Cable #3
8.46E+04
33.77
Spectrum Analyzer
2.00
-241.40
-208.97
1.27E+05
32.43
2.00
-241.40
-213.76
4.21E+04
27.64
1.00
-238.80
-209.68
1.08E+05
29.12
8.00
-241.60
-204.04
3.94E+05
37.56
PowerTx(dBm) = Pmeasured(dBm) + Lspace(dB) – Gantenna(dB) – Gamplifier(dB) + Lcables(dB)
7
Shield Effectiveness Evaluation
8
Shield Effectiveness Evaluation
9
Shield Effectiveness Measurement Standard
10
Shield Effectiveness Evaluation
Highlights of the Test Procedure:
1. Obtain Reference Measurements at distance D.
2. Receiver set to MAX HOLD while moving Rx
antenna in a plane parallel to enclosure surface at
distance D.
3. Many Measurement locations for most reliable
results and to identify problem areas.
11
Thank You!
12