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Tilting the boom on HF beam
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by AB5XZ on April 30, 2004
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I may be crazy, but I think I saw a contest rule somewhere that prohibited tilting the boom on an HF beam, presumably to control takeoff angle. Searching around, I have found one statement (from ARRL labs) that antenna height strongly affects takeoff angle.
Has anyone else ever seen a contest rule about tilting the boom?
This is purely theoretical, because there's no HF beam in my present or future hamlife.
73Tom
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RE: Tilting the boom on HF beam
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by w8car on May 1, 2004
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Tom, I have been contesting for over 30 years and have never seen a rule about tilting antennas. The angle of radiation is most influenced by height above ground or polarization (vertical or horizontal) and if tilting beams worked all the pictures of Big Gun stations would show tilted beams! Many people use wire beams hung from towers and trees and I'm sure many are tilted just because that is the only way to get them up.
Dan
W8CAR
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RE: Tilting the boom on HF beam
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by AB5XZ on May 1, 2004
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Dan,
I agree. I've never seen a pic of a big gun station with a boom tilting mechanism.
The QST question/answer said that in HF work, the height above terrain is what has the greatest effect on shaping the lobes. The "doctor" said that a tilted Yagi would be (sort of) reflected below the ground plane, and thus would cancel out any effect of boom tilt in shaping the lobes (and changing the takeoff angle).
On the other hand, anyone doing satellite work at VHF is going to want to tilt the boom(s) to point the lobes at the target. Perhaps in that case the array is far enough above the ground that the ground doesn't distort the lobes.
I would bet that the story at 10m and 6m is an interesting mixture of the two effects (height and tilt).
Well, it's an interesting mental exercise anyway.
73TomAB5XZ
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RE: Tilting the boom on HF beam
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by N0FP on May 16, 2004
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Take off angle is only influenced by the height above ground or whatever reflecting surface is involved.
Any antenna, a dipole, beam, whatever, that is horizontally polarized, will radiate in all elevations at once. Straight up, straight down, at the horizon, etc. These are the 'direct rays' coming off the wire. When the 'reflected' rays bouncing off ground combine with the direct rays, you will experience some elevations that are combined with a positive influence, and other elevations that are combined to have a negative influence. This is what forms the typical antenna elevation pattern.
A dipole and a yagi at the same height have the same take-off angle. Tilt the boom all you want on the yagi and all you have done is change the height on some elements.
There are no rules to any contest I am familiar with that limit the antenna configuration in any way.
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RE: Tilting the boom on HF beam
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by wa4dou on June 9, 2004
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From what I've read, tilting the boom raises the elevation angle and never lowers it.
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