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EMC Evaluation at Green Bank: Emissions and Shield Effectiveness

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.

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EMC Evaluation at Green Bank: Emissions and Shield Effectiveness

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  1. EMC Evaluation at Green Bank: Emissions and Shield Effectiveness National Radio Astronomy Observatory • Carla Beaudet • Green Bank RFI Group Leader

  2. 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

  3. 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! 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!

  4. Emissions Evaluation: Practical Limitations and Policy • Zone 1Policy: • No transmitters except 43MHz site radios. • All Installed Electronics must comply with ITU-R RA.769 • No electronic toys; use of electronics must be work-related. (~50K visitors/year) Zone 2 Policy: • No transmitters! (except site radios) • Electronics that will be mitigated to comply with ITU-R RA.769 include: • Anything that cannot be easily powered off • Anything that radiates in excess of FCC part 15 class B levels.

  5. Emissions Evaluation: Assessing Equipment for Compliance with ITU-R RA.769 Amplifier Receive (Rx) Antenna Equipment Under Test (EUT) Cable #1 Cable #2 Distance (Dtest) Spectrum Analyzer Cable #3 PowerTx(dBm) = Pmeasured(dBm) + Lspace(dB) – Gantenna(dB) – Gamplifier(dB) + Lcables(dB)

  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 Amplifier Receive (Rx) Antenna Equipment Under Test (EUT) Cable #1 Cable #2 Distance (Dtest) Spectrum Analyzer Cable #3 PowerTx(dBm) = Pmeasured(dBm) + Lspace(dB) – Gantenna(dB) – Gamplifier(dB) + Lcables(dB)

  8. Shield Effectiveness Evaluation

  9. Shield Effectiveness Evaluation

  10. Shield Effectiveness Measurement Standard

  11. Shield Effectiveness Evaluation Highlights of the Test Procedure: • 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.

  12. Thank You!

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