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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
The county or counties that are marked with hash markings
will receive alert tones from the transmitter. If your receiver
is capable
you can program the device to alert you when the transmitter
sends alert messages. Use the SAME code listed in the county
coverage
to program your reciever for the county or counties to
recieve alerts. |
