Base Antenna – Are you getting valuable coverage?

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When the 27 mc, CB operator looks to improve his coverage, his thoughts should turn to a more effective antenna system.

We naturally assume that most operators are running their rigs at the legal five watts input, and are probably enjoying between two and three watts output. In any event, if you are going to “soup up” your transmitter, the rig is not the place to start! After all, as the following chart shows, you would have to go to twenty watts input to increase your signal at the other fellow’s receiver by one measly S unit, and to increase your received signals by two S units, you must increase your input power to eighty watts!

antennaThe antenna, however, is a different story. Regardless of the type of antenna in use at your base station, its performance is dictated entirely by a simple set of installation procedures which you probably have not followed. The net result could be a diagram, which shows seventy-five percent of the radiated energy (signal) leaving your antenna at an angle of twenty degrees or more above the horizon. Obviously, this energy may make you sound like gangbusters in Winnipeg, but it doesn’t do a thing for your direct-wave coverage! And direct-wave (sometimes called ground-wave) is what you are after.

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So how do you bring the bulk of your radiated energy “down out of the sky” and back to earth, as in diagram two? Legally this is a tough question to answer. You see the fact that the majority (or any substantial part) of your signal energy is radiating off into the sky, and not along the ground, is determined almost completely by how high above ground your antenna is. If the base of your antenna is less than thirty-six feet and two inches above the ground (don’t run out to look…. If you are legal, it is much less). You might well be squirting more of your energy up and out (as shown in the first diagram,) than just plain out as shown in diagram two. This is due to what is termed “ground reflection” which enter the picture when an antenna is mounted less than a full electrical wavelength above ground. Ground reflections act like re-enforcing waves which “push” the normal parallel to the earth waves “up” into the ionosphere. The only way to get away from nauseating ground reflection problems is to raise the antenna up to the height above ground where the ground reflections become too weak to materially affect the radiated signals. This magical height is one wavelength, which in turn is slightly over thirty-six feet in free space.

antennaMind you, we aren’t advocating breaking the existing antenna height regulations spelled out so clearly in part 95. We are noting, however, that if you have a ground plane, vertical coaxial sleeve antenna, or beam antenna, and you have a legal means of getting its base thirty-six feet or more above ground, you do stand a much better chance of cutting down on sip interference, AND, really improving the efficiency of your direct wave coverage.



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