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antenna close to metal roof: effects?

Jan 9th, 14:52

KO0Y

Joined: Apr 7th 2012, 19:22
Total Topics: 0
Total Posts: 0
I am planning to put up a 3-wire terminated folded dipole and have a question about placement. I have a mast made of aluminum sections with a total height of up to 45 feet. I would like to fasten the lower sections to my roof at the eaves, guy the sections above, and run the antenna as an inverted-vee from the mast head with an angle between the legs of around 90 degrees. The center of the antenna would be about 38 feet above the eave (34 feet above the peak which is 14 feet away horizontally) and the antenna would run about five feet from the corner of the roofline as it descended toward the ground. The ends of the antenna would terminate about 13 feet above the ground, being fastened to trees or stakes with rope. I hope this makes sense.

The thing is, I have a metal roof, the kind that consists of curved pieces that look and feel like stone-coated tiles, and I wonder what if any effect this would have on the antenna’s performance. The antenna would not be above the roof, but rather parallel to it.

I could site the mast farther from the house and guy it to the ground, but fastening it to the roof would be much more secure. Is the close presence of a metal roof likely to degrade the antenna’s performance, or change its impedance? If so, how far away from the roof should I place the mast to avoid any degradation? Thanks for your input.
Jan 9th, 15:34

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

While not the same as your case, this ham has modeled the effect of roof with large metal panels.
https://www.qrz.com/db/OE1VMC/

Zack Lau W1VT
ARRL Senior Lab Engineer

Jan 9th, 18:31

KO0Y

Joined: Apr 7th 2012, 19:22
Total Topics: 0
Total Posts: 0
Thanks, Zack; that page is helpful. I'm going to try it fastened to the eave, as being more secure and closer to my shack. We are getting a capful of wind today, enough to blow semi-trucks over down on I-25. My current mast is guyed in three places and is swaying a bit, but so far standing. I lost our doormat, however, blown down the mountain apparently.

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