An Efficient Vertical
Vertical antennas have gotten the reputation of being less efficient than any other type of antenna. They are commonly considered to do an equally poor job of radiating in all directions. Two points in their favor are low angle of radiation and their omnidirectional pattern. Low angle radiation is better for working DX even if it is launched in a full 360 degree arc.IMPROVING EFFICIENCYThe fact that the vertical distributes RF in all directions makes it even more important to ensure that all the RF is delivered to the antenna. For a normal quarter wave vertical this requires multiple ground radials. Contrary to what some may want to believe, a good vertical is not a cheap antenna. The virtual portion of the quarter wave vertical that is supposed to be taken care of by the ground system will not work well unless the ground system uses extensive radials. A poor ground and radial system will distort the radiaton pattern and also waste RF power in resistive losses.THE VERTICAL DIPOLEThe problems associated with poor radial systems and resistive ground losses can be avoided by vertically orienting a standard dipole. The inherent balance of such a system eliminates the need for radials, but it requires a vertical that is twice the height of the standard quarter wave vertical. This generally limits its use to the higher frequency bands. Such a vertical for 20 meters will be 33 feet tall.TRAP VERTICALSThe 'all band' trap vertical is perhaps the least efficient of any vertical antenna and should be avoided. On the lower frequencies the traps act as loading coils. Unless the Q of a loading coil is very high (more than 15) there will be a significant loss of RF power in coil resistance. Since these antennas are generally of quarter wave design, they also suffer from less than perfect radial systems.COUNTERPOISED VERTICALSIf we take a vertically oriented dipole and extend one quarter wave leg vertically with the other extended horizontally, we have a counterpoised vertical. While this configuration is not as good as a true vertically polarized dipole, it is much better than a trap vertical. Such a system can be fed with open wire line and made to cover multiple bands by using an antenna tuner.
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Last updated Sep-2006
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1996-2006, by Frank Kamp, all rights reserved.