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Author Topic: Forests and beam antennas  (Read 1100 times)
VP9HW
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Posts: 18




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« on: October 06, 2010, 10:58:35 AM »

Hi,
I live in a forested area and plan to use a Moxon antenna in a small clearing surrounded by high trees. How large should the area arround the beam be. Would the trees affect the radiating pattern significantly?

Cheers de Steve (vp9hw)
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WA3SKN
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Posts: 5558




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« Reply #1 on: October 06, 2010, 11:44:26 AM »

Trees will not really affect HF, height will be the main factor.  At VHF/UHF leaves will affect the signal somewhat, so can heavy rain.  I assume the Moxon is designed for HF.
73s.

-Mike.
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K2QPN
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Posts: 70




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« Reply #2 on: October 06, 2010, 01:54:48 PM »

I have a broadband Hexx Beam (20-6 meters) at 25 feet. It is surrounded by trees that are at least 10 feet taller. Some branch are fairly close. I had to trim some to put up the antenna. Bottom line - works great. Trim what you can and go for it.

73, Bob K2QPN
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W4VR
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Posts: 1198


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« Reply #3 on: October 06, 2010, 02:11:28 PM »

As long as the branches don't touch the wires.  I remember doing some experiments at 2 GHz with trees in the way of the radiated signal and there was plenty of attenuation.  At HF it's an infinitesimal amount.
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N4JTE
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Posts: 1160




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« Reply #4 on: October 06, 2010, 02:58:05 PM »

I guess my only question would be is how close are the trees and how high are they versus your antenna ? As stated, height is the most important variable in horizontal antennas. All I know is all my wire antennas on 40 and 80 seem to work better when winter arrives and the leaves leave so to speak. Impossibe to measure the negative effect from a fully blossomed tree in front of a 40 meter moxon or maybe just the usual upbeat in signal to noise during winter, at least on 40 and 80 when trees thin out. Or it could be the usual 2 feet of snow providing a nice reflective ground plane under the wires, hi.
Build it and get er done, unless you had a 4 ele at 100 ft. in your previous experience you will do fine and the moxon will serve you well if you build it extremely close to spec. meaning the the return lengths and seperation. Less foward gain on a moxon in order to provide a smaller footprint and very good front to back for a 2 ele. wire.
Regards,
Bob
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KI4SDY
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Posts: 1452




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« Reply #5 on: October 08, 2010, 06:17:44 AM »

In cases of HF, usually the antenna can't see the forest for the trees!  Grin
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