Environmental Engineering Reference
In-Depth Information
The following calculations of the observed signal scatter ratios for the signal records in
Figures (9-4a) and (9-4b) will illustrate the use of Equations (16) to analyze test data:
From preliminary measurements at the wind turbine site,
P
WT, D
= -21.0
dB.
(a)
For the antenna aimed at the wind turbine, Figure (9-4a), let
Z
O
=
Z
O, W
and
D =
P
R
,
max
-
P
R
,
min
= - 74.5 - (-89.5) = 15.0 dB
m
R
= 0.0620D(1 - 0.0169D) = 0.695
P
R
,
mean
=
P
R
,
max
/(1 +
m
R
)
2
= 10 log
10
[10
-
7.45
]/(1.695)
2
] = -79.1dB
F
A
,
W
= [
P
R
,
]
W
/
P
R
,
mean
= -79.1 - (-79.1) = 0dB
mean
from which
Z
O
,
W
= 10 log
10
(
m
R
) + 0.5(
P
R
,
mean
-
F
A
,
W
-
P
WT
,
D
= -27.6dB = 0.0017)
(b)
For the antenna aimed at the transmitter, Figure (9-4b), let
Z
O
= Z
O, T
and
D = - 64.7 - (-65.2) = 0.5dB
m
R
= 0.0620 ´ 0.5(1 - 0.0169 ´ 0.5) = 0.031
P
R
,
mean
= 10 log
10
[10
-
6.47
/ (1.031)
2
] = -65.0dB
F
A
,
W
= -79.1 - (- 65.0) = -14.1dB
from which
= 10 log
10
(0.031) + 0.5[- 65.0 - (-14.1) - (- 27.0)] = -27.1dB = 0.0020
Z
O
,
T
Thus, as expected,
Z
O, W
»
Z
O, T
and
Z
O
is independent of the aiming point of the antenna.
In this case, the turbine scatters about 0.2 percent of its incident field onto the receiver.
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