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Electromagnetic Interference from Wind Turbines on Onsala Space Observatory

Electromagnetic Interference from Wind Turbines on Onsala Space Observatory. Eskil Bendz Johan Malmström ÅF-INFRASTRUKTUR AB. Outline . Introduction The Saab report Methods to calculate interference levels Main results The ÅF report Assessment of Saab report

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Electromagnetic Interference from Wind Turbines on Onsala Space Observatory

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  1. Electromagnetic Interference from Wind Turbines on Onsala Space Observatory Eskil Bendz Johan Malmström ÅF-INFRASTRUKTUR AB

  2. Outline • Introduction • The Saab report • Methods to calculate interference levels • Main results • The ÅF report • Assessment of Saab report • Other important considerations

  3. Introduction 34 Wind Turbines focus is the 10 encircled UMTS Radio Base Stations Purpose: Estimate and compare interference levels from direct signals and scattered signals [dBW/m2/Hz] 18 km Space Observatory

  4. The Saab report Approach: • Calculate direct signals from UMTS radio base stations • Calculate scattered signals from wind turbines • Compare the two levels of interference at Onsala

  5. Direct Signals Method: • Contribution from nearby radio base stations • Free space path loss at 2 GHz • Extra attenuation due to terrain profile (heights and vegetation) • Summarize all signals • Spectral power density: -132 dBW/m2/Hz

  6. Scattered Signals Method: • Divide wind turbine into two parts: • Tower - conical cylinder • Blades – elliptical cross section • Material – perfect electric conductor

  7. Scattered Signals Method: • Spherical wave • Scattering cross section from each segment

  8. Scattered Signals Method: • Calculate contribution from base stations close to the 10 wind turbines • 10 towers - spectral power density: -164 dBW/m2/Hz • One blade - spectral power density (maximum): -164 dBW/m2/Hz

  9. Main results • Both signals above recommended -250 dBW/m2/Hz @ 2 GHz • Direct signal is 32 dB higher than scattered signals (~1500 times) • or Scattered signals increase interference level <0.1%

  10. The ÅF report • Assessment of the Saab report found no severe errors • Simplifications overestimated the direct signals E.g. down-tilt reduce direct signals in the Saab report 6-8 dB

  11. Adjusted signal levels • New values: • Direct signal: -142 dBW/m2/Hz (Saab: -132 dBW/m2/Hz) • Scattered signals: -159 dBW/m2/Hz (Saab: -164 dBW/m2/Hz) • Direct signal still 17 dB higher than scattered signals (~50 times)

  12. Other important considerations Direct emission from radio base stations contributes largely to the interference level • E.g. UMTS, GSM, LTE • Direction of antennas • Usually three antennas at a site, covering 120 each • Suggestions to decrease interference level: • Turn off sectors • Rearrange antenna directions to obtain a ”zero” • Rearrange antenna away from telescopes • Increase down-tilt (10 might be obtained) • In accordance with mobile telephone service providers

  13. Other important considerations Some other sources that might contribute to the interference level are: • Neighboring radar stations (high power sources) • Wireless radio links (narrow beam width) • Harmonics or intermodulation products

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