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.
• 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.
• 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.
  • Signal level of greater than 18dBuV: Reliable coverage

    Green: Normal
    Orange: Degraded
    Red: Out of Service