User manual

A-4 Appendix A: Path Evaluation Information
Moseley SL9003Q 602-12016 Revision G
K factors of 1 are equivalent to no ray bending, while K factors above 1 are equivalent to ray
bending away from the earth's surface and K factors below 1 (earth bulging) are equivalent to
ray bending towards the earth's surface. The amount of earth bulge at a given point along the
path is given by:
h = (2d1xd2)/3K
Where,
h = earth bulge in feet from the flat-earth reference.
d1 = distance in miles (statute) from a given end of the microwave path to an arbitrary point
along the path.
d2 = distance in miles (statute) from the opposite end of the microwave path to the same
arbitrary point along the path.
K = K-factor considered.
Three K values are of particular interest in this connection:
1. Minimum value to be expected over the path. This determines the degree of "earth
bulging" and directly affects the requirements for antenna height. It also establishes the
lower end of the clearance range over which reflective path analysis must be made, in
the case of paths where reflections are expected.
2. Maximum value to be expected over the path. This leads to greater than normal
clearance and is of significance primarily on reflective paths, where it establishes the
upper end of the clearance range over which reflective analysis must be made.
3. Median or "normal" value to be expected over the path. Clearance under this condition
should be at least sufficient to give free space propagation on non-reflective paths.
Additionally, on paths with significant reflections, the clearance under normal conditions
should not fall at or near an even Fresnel zone.
For most applications the following criteria are considered acceptable:
K = 1.33 and CF = 1.0 F1
K = 1.0 and CF = 0.6 F1
K = 0.67 and CF = 0.3 F1