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
f
log
20
10
d
log
+
+
=
F
n
nd
1
d
2
⋅
fD
--------------------
17.3
=
RSSI
EIRP
α
–
fs
G
ra
L
rfl
–
+
=
FProb
a
b
6.0
10
7
–
f
d
3
10
F
–
(
)
10
⁄
×
×
×
×
×
×
=
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