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Author Topic: VHF/UHF mag mount antenna in attic?  (Read 2463 times)
W2BCD
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Posts: 32




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« on: January 28, 2013, 06:25:01 PM »

I got curious looking around my attic while putting the christmas decorations back up into storage. Up there is the central air unit and all its metal ducting. Would the ducting be a decent ground plane for say a mag mount mobile antenna stuck up there as a secondary option for use with my ht? I am in the basement and I can get the local repeaters in some spots while standing, but i get scratchy performance while sitting, sometimes i can transmit but not hear. And on the emergency channels sometimes i lose receive entirely. I already have the ht and mobile, and coax and an antenna are FAR cheaper then getting a whole dedicated home radio by the order of several magnitudes haha (at least the hf/vhf/uhf rigs I want!)

Second option I was thinking was one of the aluminum or copper tube dual band jpoles... they advertise no need for a groundplane which i guess would be best if i could just tie it to a beam in the attic and not have to worry about setting down metal plates anywhere.
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K7KBN
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« Reply #1 on: January 28, 2013, 06:28:09 PM »

Try it and see.
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73
Pat K7KBN
CWO4 USNR Ret.
W8JX
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Posts: 5768




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« Reply #2 on: January 28, 2013, 06:45:07 PM »

I got curious looking around my attic while putting the christmas decorations back up into storage. Up there is the central air unit and all its metal ducting.

I have used a metal cookie sheet for this once and it worked fine.
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WB6BYU
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Posts: 13242




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« Reply #3 on: January 28, 2013, 06:46:39 PM »

Inside the attic usually isn't as good as all the way outside, but often it is adequate
for a lot of local repeaters and such.  A good first test is to take your HT up there
and see how well it works.  Performance depends a lot on the roofing material and
building construction:  metal roofing and stucco walls can be problematic, while
wood shingles are relatively transparent to RF.

If you already have a mag mount, go ahead and try sticking it to a large piece of
ducting and see how it works.  Otherwise building a simple ground plane antenna
on the back of a coax connector is cheap and easy, and will probably work at least
as well as anything else you might put up there.

Something like this:  http://www.hamuniverse.com/2metergp.html
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ONAIR
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Posts: 1741




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« Reply #4 on: January 28, 2013, 08:54:17 PM »

If you have an air conditioner outside a window, try sticking the antenna on it.  Otherwise, you can just try a piece of sheet metal mounted in some fashion outside of your window or on the roof.  If you'd like to experiment, it's easy to build a 2 Meter or 440 ground plane for only a few bucks!
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N7DMA
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Posts: 18




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« Reply #5 on: February 03, 2013, 12:01:58 PM »

I have some sort of Diamond dual band mobile antenna mounted to a Larsen magnetic mount, attached to a cookie sheet in my attic, and get great coverage with it. It's my main FM antenna, and also as a backup on SSB (some folks on our 2m SSB net are vertically polarized).

This antenna replaced my Larsen NMO-150, because the cookie sheet didn't provide a very good ground plane. The Diamond is 1/2 wave on 2m, so no GP required. The NMO-150 is now on the truck.

Works for me!

Karl
N7DMA
Tucson, AZ
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KQ6Q
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Posts: 976




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« Reply #6 on: February 03, 2013, 09:52:33 PM »

be sure to use low loss coax from the basement to the attic - at least no more RG-58 than came with the mag mount. RG-8X as a minimum, or even TV type RG-6 will be low loss, even with a slight impedance mismatch. you can get adapters at Radio shack to mate RG6 F-connectors to BNC and PL-259's.
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W3HKK
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Posts: 596




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« Reply #7 on: February 04, 2013, 01:55:13 PM »

You need vertical polarization on 2m FM and I ebt your attic will work surprisingly well. Like was said, metal roof and /or stucco with wire mesh  beneath it covered with plaster will kill an otherwise good idea.

And the long run of cheap coax will  lose as much as you gain.  Good catv coax isnt  too expensive.  A couple of properly located holes to run as short a coax line as possible will pay dividends.

Good plan. Check it out!
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