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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