Draft National Wind Farm Development Guidelines - July 2010

Identify potentially affected services
Having determined the licensed services in close proximity to the wind farm, received any
early community input and reviewed any known exclusion zones for the organisations listed
above, proponents can determine which services may be affected by the wind farm
development.
This involves a calculation of the distance between line-of-sight radio paths and the
proposed wind farm, down to individual wind turbines if necessary, for any turbine
(including blades) within a line-of-sight radio path or within close proximity to a broadcast
site or if it may impact on the performance of a radar facility.
The following distances are considered to be general exclusion zones outside which a wind
turbine will not interfere with a radiocommunications service:
• Obstruction to a radio line-of-sight path
This is when the location of a wind turbine causes radiocommunications signals to be
partially or fully obstructed, resulting in a reduction or loss of signal.
It is generally accepted that effects from obstruction by wind turbines can be
avoided by placing the turbines, including blades, outside the second Fresnel Zone of
the line of sight path of a point to point radio link. This is a conservative approach.
The second Fresnel zone at any point can be calculated and is dependent upon the
frequency of the signal, the length of the radiocommunications path, and the
distance of the particular point in question along the radiocommunications path.
The maximum second Fresnel zone distance of a link occurs at the mid point along
the path.
The formula for calculating the second Fresnel zone distance at any given point is:
F2 =
2λ
d d
1
1
2
2
d + d
where
F2
λ
= Second Fresnel zone radius
= Wavelength in metres
d1, d2 are distances from each end of radio path to the point under
consideration
• Obstruction to radar services line-of-sight
Radar services may be affected by wind turbines hundreds of kilometres away if they
are located within the radar operating range and line of sight.17 As a guide, long
range 23cm (1300MHz) radars, such as those used for en-route surveillance, can have
an operating range in the order of 200 nmiles (radius of search volume in nautical
miles), a 10cm (3000MHz) approach radar 60 nmiles, and 3cm (9000MHz) final
approach radar 15 nmiles.
Individual radar operators will need to evaluate the development and advise
whether there may be any potential impact on their services.
• Near-field effects
This occurs when a wind turbine is located in such close proximity to an antenna that
it changes the characteristics of that antenna.
Transmitting and receiving antennas have a “near-field” zone, which requires
freedom from any object that can conduct or absorb radio waves.
17 CAP 764 provides a method for determining radar line-of-sight.
Draft National Wind Farm Development Guidelines – 2 July 2010 Page 175