Radio Coverage Maps

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The coverage maps are an approximation of what one might expect in the field. Assuming the coverage map is predicted correctly with an appropriate propagation model, the biggest cause of discrepancies with respect to real, achieved coverage are the assumed receive antenna height and receiver sensitivity. A typical coverage map (using a known, quantified transmit power, antenna height and accurate terrain database) makes assumptions on these key criteria, so the coverage experienced by different listeners/viewers may vary considerably from a map that declares a given coverage area that makes assumptions based upon average or best/worst case situations.

The Colorado DTRS coverage maps were generated using a free program called Radio Mobile. The program input information such as power and antenna height were obtained from the FCC database. Field checking some of this information showed it to be incorrect (such as antenna height). Sometimes the antenna gain is not included in the FCC database. Most sites use omni-directional antennas with gains ranging from 3dBi to 9 dBi. If the antenna gain is not listed in the database, 6 dBi is assumed. A loss of 4.5 dB is assumed in the combiner at the output of the transmitters. But the bottom line is that the FCC database contains errors and these maps reflect those errors.

The receiver is assumed to be a hand held scanner at 1.5 meters above ground, with 0 dBi antenna gain.

Based on testing of other sites[1] and field checking by RR forum members[2] the range of -106 dBm to -80 dBm was chosen for the maps.

  • Red and yellow should be a strong enough signal to receive indoors.
  • All other colors should indicate a strong enough signal to receive outdoors.
  • Using an antenna with higher gain will give much better results.
  • The maps have spotty coverage in the mountains due to terrain. If there is red coloring on nearby ridges then the signal often reflects well enough into non-colored areas.