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Increasing range - better RF grounding for low power AM transmitters

In the second of of three articles on increasing range, we'll go to ground. Low power AM broadcasters can significantly improve range by installing an effective Radio Frequency (RF) ground system. The signal leaving the antenna is only half (or less) of the potential signal output of a low power AM transmitter. A well constructed RF ground can provide the other half and increase both range and signal penetration.
     Listeners tuning in to low power AM broadcasts are usually receiving our ground wave rather than sky wave so better ground, more ground wave.  So how does a broadcaster construct an effective ground?
    A good place to start is where you're at.  A good RF ground system depends, in part, on a natural phenomenon called "ground conductivity." This refers to the electrical properties of minerals in the local soil. Knowing what kind of soil conditions you are working with can help you plan your efforts. 
     Read more at the FCC web site page titled Map of Effective Ground Conductivity in the USA. The higher the number, the easier your grounding efforts will be. One station operator in central California reported "This low power AM stuff is a snap - a base loaded antenna and a 4 foot ground rod and I'm getting a half mile range!" but his ground conductivity was a coveted "30." Those of us working with a "2" or a "4" have to do a bit more work.
    One last technical note and caution - true RF grounds should not radiate. Most conductors carrying RF current will radiate if not buried in the earth. This phenomenon means a long ground lead can cause compliance problems with the FCC.
     Instead of constructing an antenna with a ground, you might inadvertently build something engineers call an "off-center fed dipole." Building an off-center fed dipole could earn an FCC citation, like this one: FCC Citation for Excessive Ground Lead.
     The effort and expense of improving the grounding of a low power AM transmitter will pay off with a better signal.

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