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Author Topic: Vertical antenna on metal roof  (Read 6365 times)
W8LAS
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« on: January 20, 2013, 06:16:31 PM »

I need to replace the roof on my house and am considering an aluminum metal roof.  Would the metal roof be an effective ground plane or counterpoise as opposed to radials.  Antenna requirements show 3 ea., 25' counterpoises.  Just wondering if this would work with the vertical base being mounted directly to the roof, and if it would need to be centered.  Thanks
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WB6BYU
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« Reply #1 on: January 20, 2013, 06:21:47 PM »

Generally a metal roof makes a good ground system for a vertical antenna as long
as it is large enough, and the panels are bonded together well enough to maintain
good connectivity.  (You can't always rely on roofing nails for bonding, for example,
while paints and/or roof sealants can provide insulation between adjacent panels.)

An antenna doesn't need to be centered, but generally will be more omnidirectional
when it isn't too close to one side.  However, its been done with verticals mounted
on a mast on one side of a roof.

HOWEVER, this gives me pause:

Quote from: W8LAS

Antenna requirements show 3 ea., 25' counterpoises.


This sounds like one of the GAP antennas?  If so, the exact length of the "counterpoises"
are important, and they need to be insulated from ground.  This is NOT a standard ground-
mounted vertical antenna.


One other thing to keep in mind is that the base of the antenna should be mounted
fairly close to the roof or you may have problems tuning on 10m.  That's because the
length of the mast / tripod / ground lead from the feedpoint down to the roof becomes
part of the effective antenna length:  if it is too long then you can't shorten the
sections enough to tune the high frequency bands.  We had this problem on a large
metal roof where the antenna was mounted on a TV tripod.
« Last Edit: January 20, 2013, 06:23:56 PM by WB6BYU » Logged
W8LAS
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« Reply #2 on: January 20, 2013, 07:46:16 PM »

Thanks for the info.  I was speaking of a gap antenna, but would try any vertical that I can make work.  Don't know if any could be multiband.  Looking for getting on the air on 10, 15 and 20 meter.  I do have a 30 tower with a 40/80 isotron combo, but not enough room to put up a dipole in the HOA/CCR.
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WB6BYU
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« Reply #3 on: January 20, 2013, 08:19:35 PM »

There are a number of commercial verticals, using traps or otherwise that will work for
this.  The Hustler 4BTV and HyGain 14AVQ cover 10 - 40m, while the 12AVQ covers
20/15/10m.  There are other options - these are just the ones I remember offhand.
You can also use a straight whip (either aluminum tubing or a wire inside a fiberglass
fishing rod) and a remote autotuner, or other homebrew approaches including
parallel wires for each band.

If possible I'd suggesting choosing a vertical that works 40m as well, allowing you
to compare results between that and the Isotron.
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W8LAS
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« Reply #4 on: January 21, 2013, 10:56:11 AM »

Thanks so much, and 73's
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KE3WD
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« Reply #5 on: January 21, 2013, 10:57:00 AM »

There are a number of commercial verticals, using traps or otherwise that will work for
this.  The Hustler 4BTV and HyGain 14AVQ cover 10 - 40m, while the 12AVQ covers
20/15/10m.  There are other options - these are just the ones I remember offhand.
You can also use a straight whip (either aluminum tubing or a wire inside a fiberglass
fishing rod) and a remote autotuner, or other homebrew approaches including
parallel wires for each band.

If possible I'd suggesting choosing a vertical that works 40m as well, allowing you
to compare results between that and the Isotron.

I say that this is very good advice, if you haven't already purchased that GAP.  

The two examples given are REAL realworld verticals that work very well indeed when installed properly.  

Look, the aluminum roof panels are going to be totally covered with something to protect against aluminum corrosion.  Whatever the coating used, it will be electrically insulative if not at least highly resistive.  Bonding those panels together electrically would be mucho work and would also have to compromise the mfr's coating in order to affect the desired electrical conduction between all pieces or panels.  Doing such might likely void any warranties that may exist for the panels lasting.  Not recommended.  

On the other hand, mounting one of those two verticals on the ground where you can place as many radials as possible -- I do that over time, starting with as few as 8 and as more random bits and pieces of copper wire, both insulated and uninsulated, are found, I add more.  Placing a large gauge copper wire ring (or use copper tubing for the ring) around the base of the vertical installation and grounding that plus using it for the vertical's ground plane connection point makes increasing your ground plane wire array a rather easy task, accomplished by simply twisting the end of the new radial around a piece of the ring after sanding that small area shiny, then soldering with electrical solder and a propane torch. Fast.  

If things are such that a ground mounted vertical is out of the question, you've already got a tower and beam, consider mounting one of the two above-mentioned vertical types above the beam.  Here, you can often use the tower underneath as enough counterpoise, or even add a few wire radials or more at the tower base as well, good for some terrains tha may be rocky, etc.  

A simple Inverted Vee off of any tower can work the low bands like crazy, many hams can testify to that.  Feed it with balanced line and use a tuner to avoid the losses of coax and you can enjoy being a stateside Big Gun on the cheap.  This format has also been known to hold its own in the world of DX as well.  

There's a neat book, "Aerials" written under the pseudonym of Kurt N. Sterba out there.  If still in print, it is worth the read and keeping as reference.  Especially as concerns the Vertical types mentioned above.  In this book, the author points out that every single AM radio station in the country runs a vertical that is a fraction of the wavelength, often as little as 1/10th, yet by planting a good radial field and using a matching network these same stations are often heard many hundreds if not thousands of miles away when the conditions make that band work over longer distances.  Something that flies in the face of much of Amateur Radio's "common knowledge" right there.  

73
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N3JBH
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« Reply #6 on: January 21, 2013, 12:03:32 PM »

I mounted a 6 BVT on the barn roof one year for field day. That roof was 80X240 feet and all metal and can tell you it rocked !!! If i had a heated shack in there and was closer to home i use it all the time.
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RFRY
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« Reply #7 on: January 21, 2013, 03:03:13 PM »

There's a neat book, "Aerials" written under the pseudonym of Kurt N. Sterba out there.  ...  In this book, the author points out that every single AM radio station in the country runs a vertical that is a fraction of the wavelength, often as little as 1/10th, yet by planting a good radial field and using a matching network these same stations are often heard many hundreds if not thousands of miles away when the conditions make that band work over longer distances.  Something that flies in the face of much of Amateur Radio's "common knowledge" right there.

Just to note that AM broadcast stations in the US never are licensed for, or routinely use a vertical monopole, or a directional array of several such monopoles of electrical height(s) "as little as 1/10" of a wavelength.

The reason for this is that such antenna systems cannot produce the minimum r.m.s. groundwave field intensity at 1 km that is required by the FCC even for the lowest class of licensed AM broadcast station -- and even though they are using 120 x 1/4-wave buried radials, with the antenna system feedpoint perfectly Z-matched to the source.

RF
« Last Edit: January 21, 2013, 03:13:12 PM by RFRY » Logged
KE3WD
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Posts: 5689




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« Reply #8 on: January 21, 2013, 03:09:59 PM »

I mounted a 6 BVT on the barn roof one year for field day. That roof was 80X240 feet and all metal and can tell you it rocked !!! If i had a heated shack in there and was closer to home i use it all the time.

Old "tin" barn roof was often not coated and the overlapping of the sheet metal was enough to establish good conductivity between sheets.  Some were even sweat soldered along the seams to seal from water intrusion as well. Can't beat that for an electrical connection. 

On the other side of things, a metal roof consisting of multiple panels and no electrical connect between them worth mentioning can be a nightmare of noise, dissimilar junctions, and other weird anomalies for the HF enthusiast. 

The modern aluminum roofing panels as cited by the OP here are a different story entirely and establishing good electrical connect between panels can be problematic, for reasons already mentioned.

73
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KD4LLA
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Posts: 462




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« Reply #9 on: January 21, 2013, 07:51:14 PM »

I need to replace the roof on my house and am considering an aluminum metal roof.

Aluminum???  That has to be spendy.  Why not just plain steel.  It comes in many colors and textures nowadays.  They even have stuff that look like "real" shingles.

The only other problem I see is, after the price of a new roof and installation, why would you want holes in it putting an antenna up on it?

Mike
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W8LAS
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« Reply #10 on: January 23, 2013, 07:40:25 AM »

Thanks for all the feedback.  Several great suggestions.  Thanks to all of you Elmers out there.
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AD6KA
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« Reply #11 on: January 24, 2013, 03:34:35 PM »

I ran an old Cushcraft R7 on top of a metal roof
when I was in 5R8 (Madagascar). The R7 was admittedly a crappy
antenna but was a free local loaner. (One less thing that
I didn't have to haul 11,000 miles!)  Grin
It was a screamer on 10 thru 20m, fair on 40.
I won SOAB High Power Africa in the 2000
CQ WW DX RTTY Contest with it.

I too think a 5 or 6 BTV over an aluminum roof
is a good choice. Here at home I have the HF6V
over a wooden roof and elevated tuned radials.
It works very, very well. I'm very happy with it.
But the HF6V really likes a tuned radial system when elevated.
Good luck with your project!
73, Ken  AD6KA/5R8GQ
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NK7Z
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« Reply #12 on: January 25, 2013, 06:17:25 AM »

Antenna requirements show 3 ea., 25' counterpoises.

Not enough, and the length is not that critical...  I use as many redials as possible each 1/2 wave in length for any band I intend on operating...  This is one time, where more is better, up to about 16 radials...  After that, it gets better but not near as fast as the first 16...

73's
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
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