PathAlign-R
Spectracom Corporation
2200 / 2240 / 2241 PathAlign-R Manual
5-46
Dt = 3.7 miles
x = 100 feet
f = 0.880 GHz (880 MHz)
The first Fresnel zone:
R = 72v ((d1)(d2) / (Dt)(f))
R = 72v ((1.6)(2.1) / (3.7)(0.88))
R = 72v (3.36 / 3.256)
R = 73.14 feet
For 0.6 clearance from the first Fresnel zone = (73.14)(0.6) = 43.9 feet
Earth's curvature h = ((d1)(d2) / (1.5)(K))
At obstruction: h = ((1.6)(2.1) / (1.5)(4/3)) = 1.7 feet
If Tx and Rx antennas are the same altitude above sea level:
The earth's curvature: 1.7 feet
0.6 first Fresnel clearance for 880 MHz: 43.9 feet
Obstruction height: 100.0 feet
Then the minimum ht and hr (antenna height above ground): 145.6 feet.
5.3
Definitions
5.3.1 Wave Length (
λ
)
The wavelength for a microwave frequency is given as: 30 /
f
GHz =
λ
cm
Where:
f
GHz = Frequency in Giga Hertz, and
λ
cm = wave length in centimeters
e.g.: 30 GHz = 1 cm λ 20 GHz = 1.5 cm
λ
; 10 GHz = 3 cm
λ
.
5.3.2 Antenna Gain
For a paraboloid reflector microwave antenna (greater than 960 MHz) consisting of a dish-
shaped surface illuminated by a feed horn mounted at the focus of the reflector, the antenna
gain is given as [6]:
Antenna Gain
(dBi) = 20 log10(
D
ft) + 20 log10(
f
GHz) + 7.5; or,
Antenna Gain
(dBi) = 20 log10(
D
m) + 20 log10(
f
GHz) + 17.82
Where:
dBi = decibels over an isotropic radiator
D
ft = Antenna dish diameter in feet; or,
D
m = Antenna dish diameter in meters, and
