Division General principles
United Kingdom
Figure 2.5.c illustrates the general method of calculation of the attenuation due to diffraction. This method is based on breaking down the propagation path into two parts: the ‘source side’ path, located between the source and the diffraction point, and the ‘receiver side’ path, located between the diffraction point and the receiver.
The following are calculated:
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a ground effect, source side, Δ ground(S,O)
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a ground effect, receiver side, Δ ground(O,R)
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and three diffractions:
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between the source S and the receiver R: Δ dif(S,R)
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between the image source S′ and R: Δ dif(S′,R)
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between S and the image receiver R′: Δ dif(S,R′) .
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Figure 2.5.c
Geometry of a calculation of the attenuation due to diffraction
Source side
Receiver side
where
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S is the source;
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R is the receiver;
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S′ is the image source in relation to the mean ground plane source side;
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R′ is the image receiver in relation to the mean ground plane receiver side;
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O is the diffraction point;
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z s is the equivalent height of the source S in relation to the mean plane source side;
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z o,s is the equivalent height of the diffraction point O in relation to the mean ground plane source side;
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z r is the equivalent height of the receiver R in relation to the mean plane receiver side;
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z o,r is the equivalent height of the diffraction point O in relation to the mean ground plane receiver side.
The irregularity of the ground between the source and the diffraction point, and between the diffraction point and the receiver, is taken into account by means of equivalent heights calculated in relation to the mean ground plane, source side first and receiver side second (two mean ground planes), according to the method described in the subsection on significant heights above the ground.