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Free Space Path Loss
α
=
92.4
+
20
log
fs
α
= free space loss in dB
fs
d = path distance in kilometers
ƒ = frequency in GHz
Fresnel Zone Boundary
⋅
nd
d
1
2
F
=
17.3
------------------- -
n
fD
F
= Fresnel zone boundary in meters
n
d
= distance from one end of the path to the Fresnel zone boundary (in
1
kilometers)
d
= distance from the other end of the path to the Fresnel zone
2
boundary (in kilometers)
D = total path distance (d
ƒ = frequency in GHz
n = Fresnel zone, 1 (for 1st) is used here
Theoretical Signal Strength
EIRP α
RSSI
=
–
fs
RSSI = signal strength at the receiver in dBm
EIRP = RF power output in dBm + G
α
= free-space path loss in dB
fs
G
= receive antenna gain in dBi
ra
L
= receive feedline loss in dB
rfl
L
= transmit feedline loss in dB
tfl
G
= transmit antenna gain in dBi
ta
Probability of System Fading
×
×
FProb
=
a b
6.0
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
MDS 4790/9790 Series I/O Guide
f
+
20
log
d
where:
10
10
where:
+d
) in kilometers
1
2
+
G
–
L
where:
ra
rfl
–L
ta
tfl
7 –
3
×
×
×
×
10
f d
10
MDS 05-3438A01, Rev. F
– ( ) 10
⁄
F
where:
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