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

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Presentation on theme: "Eskil Bendz Johan Malmström ÅF-INFRASTRUKTUR AB Electromagnetic Interference from Wind Turbines on Onsala Space Observatory."— Presentation transcript:

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

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

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/m 2 /Hz] 3 Space Observatory 18 km

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 4

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/m 2 /Hz 5

6 Scattered Signals Method: Divide wind turbine into two parts: 1.Tower - conical cylinder 2.Blades – elliptical cross section Material – perfect electric conductor 6

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

8 Scattered Signals Method: Calculate contribution from base stations close to the 10 wind turbines 10 towers - spectral power density: -164 dBW/m 2 /Hz One blade - spectral power density (maximum): -164 dBW/m 2 /Hz 8

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

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 10

11 Adjusted signal levels New values: Direct signal: -142 dBW/m 2 /Hz(Saab: -132 dBW/m 2 /Hz) Scattered signals: -159 dBW/m 2 /Hz (Saab: -164 dBW/m 2 /Hz) Direct signal still 17 dB higher than scattered signals (~50 times) 11

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: 1.Turn off sectors 2.Rearrange antenna directions to obtain a zero 3.Rearrange antenna away from telescopes 4.Increase down-tilt (10 might be obtained) In accordance with mobile telephone service providers 12

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 13


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