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Re: [TowerTalk] End feeding a half-wave vetical

 To: "Dennis O'Connor" , Re: [TowerTalk] End feeding a half-wave vetical "Tom Rauch" Tom Rauch Tue, 2 Aug 2005 10:17:50 -0400
 ```> Jim, > My feeling is that this is much ado about very little... First, a 4 degree difference in MODELED takeoff angle on 160 is meaningless...The presence of power lines, house wiring, plumbing pipes, sewer lines, telephone wires, CATV cable, and on, and on, within the near field makes the model nothing more than a rough guide - very rough... Everything metal out to 3 waves is going to have a major effect on your pattern... >From experience... I'm in gently rolling pastureland in middle GA. I have a 318 foot insulated base tower. There is really no significant difference between that tower and a 200 ft tower or a 1/4 wl vertical. Of course I have a good ground system of 100 200 ft radials on the 200 ft tower and 50 1/4 wl radials on the 1/4 wl vertical. The problem is I don't know how things would compare with a poor ground system. My input on the model would be this: Models amateurs use generally assume FS at some very large distance from the antenna. You can tell if the model is doing this by looking at FS at zero degrees. If you see FS at zero degrees is very low or nearly zero, you know the model assumes you are interested in FS at a distance of hundreds of wavelengths or more. That really isn't how the antenna works in the real world. The real world isn't flat and on 160 meters the height of the ionosphere often compares to the distance the model uses to calculate pattern. The result of this is low angle FS is often underestimated. I think this is why good 1/4 wl verticals often compare nearly equally with high dipoles on 160 and why the two come reasonably close on 80. When I model a vertical on 160 the model shows a dipole at 300 feet would beat the vertical at almost any angle. Yet when I actually installed an ideal dipole at 300 feet and compared it to a vertical in hundreds of A-B blind tests the dipole and vertical averaged within a few dB of each other broadside to the dipole, and the vertical just naturally smoked the dipole near the ends of the dipole. A second issue would be the exaggerated use of TO angle to pick an antenna. TO angle alone doesn't matter. What matters is the absolute field strength at the desired angle or angles. An antenna can have a TO angle of 30 degrees and have more absolute FS at 10 degrees than an antenna with a TO angle of 10 degrees. Models are excellent for antennas some distance above earth, especially horizontally polarized antennas. They really are just very rough approximations for vertical antennas near earth (or even dipoles at very low height). I wouldn't predict one way or another what would happen in other locations where a marginal ground system is used, but I'd never rest 100% on any model when earth is involved...especially when the models we use don't model the earth in any accurate detail. 73 Tom _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] End feeding a half-wave vetical, Dennis O'Connor Re: [TowerTalk] End feeding a half-wave vetical, Tom Rauch <=