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Author Topic: In-wall antenna (Yagi-Uda beam on the wall)  (Read 1119 times)
LA9XSA
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Posts: 376




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« on: December 11, 2012, 04:03:28 PM »

In-wall or on-wall beam antennas.

I went to a presentation for the NUTS Cubesat ( http://nuts.cubesat.no ) where one of the presentations was about implementing UHF phasing networks and transmission lines on printed circuit boards, and I've also seen Yagi-Uda beams implemented on PCB style boards ( http://www.wa5vjb.com/products2.html )

This reminded me of an idea I had this summer: What if I hang some wires in a beam antenna pattern, on a wood wall that is perpendicular to a hard-to hit repeater, would it make a workable stealth vertical beam? The house in question has only wood sidings, the downspouts are PVC and I'd stay away from wiring. Has anyone tried this out? I tried searching online, but I can't seem to have found the right keywords.

Hiding a beam antenna in the attic is complicated by the presence of protected bats, and the metal roof material.

Stealth isn't really a requirement at my location - it's easy to get permission for antennas if needed - but it struck me as an obvious solution that I haven't found any examples of online. You'd just hang some wires next to each other on a wall, be it on the exterior or interior wall.
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K2OWK
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Posts: 1073




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« Reply #1 on: December 11, 2012, 04:17:14 PM »

I used to make cheep beams using a wood boom and wood cross pieces with the proper spacing, and copper wire attached to cross pieces. These beams worked great, and you could make and use as many elements as practical. The setup you are thinking of should work good. It sounds very much like the wood beams I used to make.

73s

K2OWK
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WB6BYU
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Posts: 13479




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« Reply #2 on: December 11, 2012, 04:46:31 PM »

The wood siding will affect the resonant lengths to some extent.  I tried some 10m
beams attached to my ceiling (wires held in place with thumbtacks) and they didn't
work very well, partly due to the dielectric effect of the gypsum wallboard.  (I've had
fewer issues with UHF antennas hanging on the inside of a glass window, though a
ground plane has a wider bandwidth to start with.)

You might consider putting the antenna on a broadside wall:  I did that with a
2m bobtail curtain using aluminum cooking foil wrapped around the coax as the
center element and it worked reasonably well.  Various sorts of bent-wire antennas
(Sterba or Bruce curtains, or other sorts of broadside arrays, for example) can
be attached flat against the wall.
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K2DC
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Posts: 1381


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« Reply #3 on: December 12, 2012, 03:24:11 AM »

I don't see why it couldn't be made to work, although BYU is correct - the wood will have an impact on element length and spacing as wood has a dielectric constant of between 1.4 and 2.9 depending on the density.  To assess the impact of the wood, you might try this:  Construct a simple wire dipole in the clear, trim it to resonance and measure the length.  Then tape the dipole against the wood wall, and trim again to resonance.  It's new length should determine the scale factor needed to shorten element lengths and spacing to get the most you can out of the yagi.

73,

Don, K2DC
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WX7G
Member

Posts: 6207




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« Reply #4 on: December 12, 2012, 06:01:32 AM »

A broadside array is what you need, not a Yagi-Uda.
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