Observability at HF direction finding sites of scattering from wind farms - measurements at Smøla 2006

This report studies, on a general basis, whether wind farms may decrease the accuracy of direction finding systems in the HF (high frequency, 2-30 MHz) band, due to scattering from the wind turbine towers or blades. Theoretical considerations are accompanied by a three-day measurement campaign at Smøla, a large wind farm with 68 wind turbines installed. The measurements provide evidence that the wind farm causes direction finding errors when it is between transmitter and receiver, but also shows errors of similar level at other angles, which are more likely attributed to topographic features than to the wind farm. Additionally, the measurements revealed an unexpected effect of much larger errors at certain positions, which seem to be modulated by blade rotation. A more comprehensive measurement campaign would be required to fully understand the observed effects.