AirLive WH-9000MESH - Manual (Page 13)

Using below Free Space Loss Formula to calculate free space path loss
D F L
P 10 10
log 20 log 20 6 . 96 + + =
Where
L
P
= free space path loss between antennas
F = frequency in GHz
D = path length in miles
2.2.2 Estimation Bridge’s antenna Location
When as bridge device, the WH-9000MESH may need to be mounted outdoors on a high place to
achieve the best bridge result. The Fresnel zone and Earth bulge dominate to decide how high that
the unit’s Antenna need be put. The total antenna height equals the width of Fresnel zone plus the
height of earth bulge.
y Fresnel zone:
The Fresnel zone is the area around the visual
line-of-sight that radio waves spread out into
after they leave the antenna. This area must be
clear or else signal strength will weaken. The
rule of thumb is that 60% of the Fresnel zone
must be clear of obstacles. Typically, 20%
Fresnel Zone blockage introduces little signal loss to the link. Beyond 40% blockage, signal loss will
become significant. The equation of the width of Fresnel Zone is
F
D
W
4
3 . 43 × =
Where
W = Width of the Fresnel Zone (in feet)
D = Distance between the antennas (in miles)
F = Frequency in GHz
y Earth Bulge
When the transmit distance of RF signal is longer than seven miles, the curvature of the earth may be a
factor and require the antenna put at higher location. The additional antenna height can be calculated
by below formula:
2
8
D
H =
Where
H = Height of earth bulge (in feet)
D = Distance between antennas (in miles)
AirLive WH-9000-MESH User’s Manual 12