Environmental Engineering Reference
In-Depth Information
Figure 9-5. Receiver modulation index as a function of the power signal modulation
range.
It is clear now that knowledge of both the direct and scattered signals at the receiver's
input terminals is necessary for the determination of
m
R
,
the receiver modulation index, and
f
m
,
the modulation shape function, associated with the total signal. The maximum expected
value of
m
R
is the basic parameter that is used to judge the acceptability of the potential
EMI with a particular receiver. Thus
m
R
, max
<
m
P
,
T
:
Impercept ible EMI
, max
³
m
P
,
T
:
Percept ible EMI
(9-13)
m
R
where
m
R, max
=
maximum expected receiver modulation index, for all possible wind turbine
rotor and blade orientations
m
P, T
= modulation threshold of perception, from studies of test subjects
Thresholds of perception will differ for different electromagnetic systems and periods of
exposure. Some guideline values for modulation perception indices will be discussed later.
Signal Scatter Ratio
The strength of the scattered signal field at a receiver location caused by a wind turbine
can be conveniently expressed as a
signal scatter ratio
,
which is the ratio of the amplitude
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