FM Transmission Systems Rockwell Media Services, LLC 158 West 1600 South, Suite 200, St. George, Utah 84770 Reprinted by permission from W.C. Alexander, Crawford Broadcasting, Director Engineering,
[email protected] FM Transmission Systems W.C. Alexander Director of Engineering Crawford Broadcasting Company IntroductionAbstract Unfortunately, the real world is very different from this ideal. The real world is The variables in any given FM full of obstructions, manmade and natural, transmission system are many. They include that partially or fully obstruct the path from factors such as antenna height versus ERP, the transmitting to receiving antenna. Real- antenna gain versus transmitter power, world transmitting antennas exhibit some vertical plane radiation patterns, Brewster non-uniformity in the horizontal plane, and angle, Fresnel zone, polarization, site in the vertical plane, half of the energy is location and topography among others. In radiated above the horizon into space, where this paper, we will examine each of these it is wasted. Reflections from objects also variables, the tradeoffs between cost and produce amplitude variations in the received performance, antenna and transmission line signal that cause noise and signal dropouts. types, installation and maintenance The number of variables that go into techniques and procedures. the performance of a particular antenna site is quite large, and many of these factors are 1.0 Antenna Site Considerations beyond the broadcaster=s control. Many can While few of us have much control be mitigated, however, with good site over the location of our antenna sites, selection, and it is on those that we must perhaps there is room for change in some focus when searching for an antenna site.