The coverage statistics
and maps are calculated using a computer model and station
data assuming ideal conditions. Coverage may be 5 to
10 percent below the computer predicted coverage for
the following reasons:
The computer model is sensitive to antenna performance.
Antenna performance is a function of local conditions,
causing signals to be stronger signal level in some
directions than others.
Most NWR stations are at existing antenna towers,
provided at little or no cost.
Placement of NWR antennas is dictated by the tower
owner, which may result in a less than ideal set up.
The antenna may be affected by nearby structures
or bodies of water.
In some special instances, the antenna may have
been intentionally adjusted to be "directional"
and provide better coverage to a specific area to
the detriment of other areas.
Most of the stations employ equipment technology
more than 20 years old. Because of variations in local
site conditions, the performance of an individual
transmitter and antenna may be less than predicted
or expected.
Seasonal environmental conditions, such as icing
or heavy rain, affect performance of a transmitter
station and its various components, particularly those
subject to continuous weather exposure.
The coverage maps are shown in a single color format,
which relates to an estimated signal level
.
White: Signal level of greater than 18dBuV:
Reliable coverage
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