Spectracom Corporation
PathAlign-R
2200 / 2240 / 2241 PathAlign-R Manual
5-45
A 'K' factor of 1 indicates no bending of the signal; a 'K' factor of less than one means the
electromagnetic wave is bent up, away from the surface. A 'K' factor greater than one indicates
a slight bending downward, towards the earth. The 'K' factor value commonly used for
microwave links is 1.333 (4/3) for normal atmospheric conditions, which means that the radio
horizon is further away than the visual horizon.
5.2.5 Link Design
Links should be designed, using the above information, to accommodate obstructions
(mountains, buildings, trees) and atmospheric conditions (large bodies of water, weather
conditions, and other natural reflectors and absorbers of electromagnetic energy).
The following image displays a typical microwave point-to-point link and the basic formulas for
reliable link design.
Figure 5-2. Typical Point-to-Point Link Design
Where:
R = Curved path of the first Fresnel zone radius (at the obstruction)(in feet)
ht = Height above the earth's surface at the transmitting antenna (in feet)
hr = Height above the earth's surface at the receiving antenna (in feet)
x = Height of obstruction (in feet)
h = Earth's curvature, from a flat plane between antennas, at the obstruction (in feet)
d1 = Distance from transmitting antenna to obstruction (in miles)
d2 = Distance from receiving antenna to obstruction (in miles)
Dt = Total path distance between antennas (in miles)
f = Transmitted frequency (in GHz)
As an example, where:
d1 = 1.6 miles
d2 = 2.1 miles
