102 MDS 4790/9790 Series I/O Guide MDS 05-3438A01, Rev. F
Free Space Path Loss
where:
α
fs
= free space loss in dB
d = path distance in kilometers
ƒ = frequency in GHz
Fresnel Zone Boundary
where:
F
n
= Fresnel zone boundary in meters
d
1
= distance from one end of the path to the Fresnel zone boundary (in
kilometers)
d
2
= distance from the other end of the path to the Fresnel zone
boundary (in kilometers)
D = total path distance (d
1
+d
2
) in kilometers
ƒ = frequency in GHz
n = Fresnel zone, 1 (for 1st) is used here
Theoretical Signal Strength
where:
RSSI = signal strength at the receiver in dBm
EIRP = RF power output in dBm + G
ta
–L
tfl
α
fs
= free-space path loss in dB
G
ra
= receive antenna gain in dBi
L
rfl
= receive feedline loss in dB
L
tfl
= transmit feedline loss in dB
G
ta
= transmit antenna gain in dBi
Probability of System Fading
where:
FProb = probability of fading more than F
a
=terrain factor
• 4 is used for very smooth terrain, such as over water
• 1 is used for average terrain, with moderate roughness
• 0.25 is used for mountainous or very rough terrain
b = climate factor
• 0.5 is used for a hot, humid climate
• 0.25 is used for temperate or northern areas
• 0.125 is used for a very dry climate
ƒ = frequency in GHz
d = path length in km
F = fade margin in dB
α
fs
92.4 20
10
flog 20
10
dlog++=
F
n
nd
1
d
2
⋅
fD
--------------------
17.3
=
RSSI EIRP α–
fs
G
ra
L
rfl
–+=
FProb a b 6.0 10
7–
fd
3
10
F–()10⁄
××××××=
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