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.