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Eskil Bendz Johan Malmström ÅF-INFRASTRUKTUR AB

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Presentation on theme: "Eskil Bendz Johan Malmström ÅF-INFRASTRUKTUR AB"— Presentation transcript:

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

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

3 Introduction Purpose: 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: 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: dBW/m2/Hz One blade - spectral power density (maximum): 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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