How accurate are the coverage maps that are found on radio-locator.com ?
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- Thread starter johnbasalla
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Realize that it is the 60, 50, and 40 dBu contours for FM. The inner contour is NOT the 70 dBu city grade contour. The contours do not take terrain shadows and terrain beyond 10 miles into account. If the land is quite flat, it is fairly accurate.
Realize that on AM it is the 2.5, 0.5, and 0.15 mV/m contours. The 0.15 is omitted in the night coverage areas. 5 mV/m is the city grade contour, not 2.5. Many areas of the country are not accurately shown on the M-3 map for conductivity, which is used to generate the contours. The signals may be much stronger in the winter than in the summer. Nearly all stations have a nightttime interference free contour in excess of 2.5 mV/m, unless they are Class A facilities. Even the inner contour may not be well heard on many stations at night. No skywave is shown, which may be useful for Class As and powerful Class Bs, though there is no guarantee for Class Bs.
The maps are useful as a general starting point, but much more information is needed for an accurate view.
Realize that on AM it is the 2.5, 0.5, and 0.15 mV/m contours. The 0.15 is omitted in the night coverage areas. 5 mV/m is the city grade contour, not 2.5. Many areas of the country are not accurately shown on the M-3 map for conductivity, which is used to generate the contours. The signals may be much stronger in the winter than in the summer. Nearly all stations have a nightttime interference free contour in excess of 2.5 mV/m, unless they are Class A facilities. Even the inner contour may not be well heard on many stations at night. No skywave is shown, which may be useful for Class As and powerful Class Bs, though there is no guarantee for Class Bs.
The maps are useful as a general starting point, but much more information is needed for an accurate view.
Schroedingers Cat said:
Amen to all of that; Mr Cat's info is correct. I have been very critical of R-L because of its inaccuracies and its misleading contours. In fact, for several years, their coverage data for FMs did not reflect directional antennas, where they were used. I believe that problem was corrected well over a year ago. To be fair to R-L, however, they now provide access to polar pattern plots of AMs' horizontal-plane electric-field intensity vs azimuth, although I don't think think you can access those plots via the usual R-L home page; the URL I have for the pattern plots is http://www.radio-locator.com/cgi-bin/ampat? . Of course, those same plots are available through the AM Query page at www.fcc.gov and also elsewhere on the Web.
Schroedingers Cat said:
Good point. In the real world, about 95% of all in home and at work FM listening to rated market stations takes place in the 64 dbu contour, and about 80% in the 70... both well inside the red inner contour at RL. 70% of listening is in those locations, not in the car.
On AM, very little in home and at work listening in metros occurs outside the 10 mV/m contour, with some noisy places like LA finding the 15 mV/m to be where 90% of AM listening takes place.
The public's tolerance for bad signals is very low.
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