Electromagnetic Compatibility at Green Bank: Evaluation and Mitigation National Radio Astronomy Observatory John Ford Green Bank Electronics Division Head Carla Beaudet Green Bank RFI Engineer
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 specifies allowable field strength at a given distance. Translates to Radiated Power of Device
Emissions Evaluation: Practical Limitations and Policy Dream On Options for not creating self-interference: 1000km! radius electronic device-free zone!!!! Contain all electronic equipment on site ALL? Really? electronic position with large enclosures, equipment on site withorlarge enclosures, facilities behind natural obstacles. or position facilities behind natural obstacles. Use a practical (compromise) approach, policy and adhere to it!approach, but Use set a practical (compromise) but set policy and adhere to it!
Emissions Evaluation: Practical Limitations and Policy Zone 1Policy: Policy: No transmitters transmitters!except (except 4MHz site radios) site radios. All Electronics Installedthat Electronics will be must mitigated comply to comply with ITU-R with RA.769 ITU-R RA.769 include: No Anything electronic thattoys; cannot usebe of electronics easily powered mustoff be work-related. (~50K Anything that radiates in visitors/year) excess of FCC part 15 class B levels. 4
Communicating Site Policy 5
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 10.1 1.4-64.00 0.010 0.0100 CW -14.00 70.9 1.11-71.00 0.010 0.0100 CW -141.00 Receive (Rx) Antenna Equipment Under Test (EUT) 4 154.8 1.94-66.50 0.010 0.0100 CW -16.50 94.98 0. -67.0 0.010 0.0100 CW -17.0 Amplifier Cable #1 Test Setup and Total Radiated Power Per Unit RBW Measured During Test Test Antenna Number ( Select 1,,, 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 ).7 0.8 1.10 5.0 7.00.06-154.14.7 0. 1.10 5.0 7.00 4.7-158.9.00 0.47 0.80 5.0 7.00 1.14-157.86 6.06 0.0 4.70 5.0 7.00 4.61-14.19 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 Cable # Distance (Dtest) Predicted Impact on GBT Observations Spectrum Analyzer Cable # 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 ).00-44.50-10.7 8.46E+04.77.00-44.50-15.5.81E+04 8.98 1.00-41.00-09.68 1.08E+05 1. 0.00-48.80-08.0 1.58E+05 8.78.00-41.40.00-41.40 1.00-8.80 8.00-41.60 wertx(dbm) = Pmeasured(dBm) + Lspace(dB) Gantenna(dB) Gamplifier(dB) + Lcables(d Predictions for SPECTRAL LINE OBSERVATIONS Corresponding Target GBT SPECTRAL LINE Bandwidth ( MHz ) Corresponding Target GBT SPECTRAL LINE Limit ( dbw/m*m/hz ) 6
Emissions Evaluation: Assessing Equipment for Compliance with ITU-R RA.769 Faraday Cages Low-Pass Filters RF Absorber 7
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 10.1 1.4-64.00 0.010 0.0100 CW -14.00 70.9 1.11-71.00 0.010 0.0100 CW -141.00 Receive (Rx) Antenna Equipment Under Test (EUT) 4 154.8 1.94-66.50 0.010 0.0100 CW -16.50 94.98 0. -67.0 0.010 0.0100 CW -17.0 Amplifier Cable #1 Test Setup and Total Radiated Power Per Unit RBW Measured During Test Test Antenna Number ( Select 1,,, 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 ).7 0.8 1.10 5.0 7.00.06-154.14.7 0. 1.10 5.0 7.00 4.7-158.9.00 0.47 0.80 5.0 7.00 1.14-157.86 6.06 0.0 4.70 5.0 7.00 4.61-14.19 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 Cable # Distance (Dtest) Predicted Impact on GBT Observations Spectrum Analyzer Cable # 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 ).00-44.50-10.7 8.46E+04.77.00-44.50-15.5.81E+04 8.98 1.00-41.00-09.68 1.08E+05 1. 0.00-48.80-08.0 1.58E+05 8.78.00-41.40.00-41.40 1.00-8.80 8.00-41.60 wertx(dbm) = Pmeasured(dBm) + Lspace(dB) Gantenna(dB) Gamplifier(dB) + Lcables(d Predictions for SPECTRAL LINE OBSERVATIONS Corresponding Target GBT SPECTRAL LINE Bandwidth ( MHz ) Corresponding Target GBT SPECTRAL LINE Limit ( dbw/m*m/hz ) 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.. Receiver set to MAX HOLD while moving Rx antenna in a plane parallel to enclosure surface at distance D.. Many Measurement locations for most reliable results and to identify problem areas. 11
Thank You! 18