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Author Topic: Vertical antenna near metal structures  (Read 3190 times)
N5GZH
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Posts: 87




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« on: October 02, 2013, 02:01:48 AM »

I'm in the process of putting up a neighbor-conscious antenna at my  location and it's looking like a 31 ft. ground mounted vertical (S9V31) may be an option.  In addition to horizontal aluminum gutters and downspouts about 20 feet from the antenna, there is also an 8" diameter vertical stove pipe, running from about ground level to 12 feet high and located roughly 25 feet from where the antenna needs to go.

My question:  Any chance of working off of any of this "stuff" as ground ?  I can probably remove a good 6 feet of the stove pipe if necessary.  I'm also thinking about replacing some of the aluminum gutters with  plastic ones.   I expect these blasted things to change the tuning of the antenna and this is likely not a problem.  Just wondering how much RF they are likely to soak up ?
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K2DC
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« Reply #1 on: October 02, 2013, 02:13:51 AM »

The horizontal gutters are unlikely to have much impact at all.  The downspouts and stove pipe may have some impact, but its difficult to say how much without careful modeling and/or extensive testing with and without them.  If it were me, I'd just throw it up and see if it did what I needed it to do.

73,

Don, K2DC

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N5GZH
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Posts: 87




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« Reply #2 on: October 02, 2013, 02:18:52 AM »

The horizontal gutters are unlikely to have much impact at all.  The downspouts and stove pipe may have some impact, but its difficult to say how much without careful modeling and/or extensive testing with and without them.  If it were me, I'd just throw it up and see if it did what I needed it to do.

73,

Don, K2DC



Don, that's music to my ears.   Smiley
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WX7G
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« Reply #3 on: October 02, 2013, 03:16:41 AM »

The stove pipe and gutters will have significant RF current if they are resonant near an amateur band. The AC wiring inside the house will also have RF current if it is resonant near an amateur band.

An EZNEC simulation of the worst case loss - a 31' stove pipe having a ground loss of 50 ohms - shows a system loss of only 1 dB.



« Last Edit: October 02, 2013, 03:20:21 AM by WX7G » Logged
M5AEO
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Posts: 273




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« Reply #4 on: October 02, 2013, 04:16:05 AM »

Hi N5GZH!

I have a home-brew vertical on my apartment balcony.  The antenna itself is mounted on metal railings and there is significant metal work all around, such as roofing materials etc.
However, against all the odds, it does radiate; I have managed to work VK on SSB.  I don't even seem to cause any TVI either, although I tend to run only 50 watts; I guess if you are using an amp there may be more of an issue.
73s
Jonathan M5AEO, London.

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N5GZH
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« Reply #5 on: October 02, 2013, 06:28:37 AM »

Great advice here !  Many thanks.
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K8AXW
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« Reply #6 on: October 02, 2013, 06:48:11 AM »

GZH:  I'd do as Don suggested...."throw it up, etc."  Too many times we hams tend to over-think some of these situations, rather it's an antenna or a linear.

Back in the olden times, we used to "do it" and then see if we had a problem.  If we did, we kept changing whatever until there wasn't a problem.

Of course there are some things, like towers, guy wires, and such that require considerable planning and consideration.  But most of the time, the best thing is to "git 'er done."
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G3RZP
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« Reply #7 on: October 02, 2013, 01:54:47 PM »

there's an old UK saying (definitely capable of mis-interpretation these days!) of 'Suck it and see'.
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K8AXW
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« Reply #8 on: October 02, 2013, 06:53:28 PM »

Peter:

Quote
Suck it and see

 Grin
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