Attic dipole

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jquittum

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Would an 11 meter dipole 20 feet above ground but in the attic with asphalt shingles, work any better than the same antenna only 5ft above ground but outdoors?
 

wyShack

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For 'local' work, the greater height will give you quite a bit more 'line of sight' range-as long as the roof doesn't attenuate the signal. In both cases, you may have an issue talking with stations using vertical polarization- the cross polarization loss (assuming 11 meters) could be as much as 20-30 Db-which would be several 'S-units'. For other situations the greater height will lower the 'radiation angle' meaning more signal will hit the ionosphere at usable angles.

Hope this helps.
 

jquittum

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For 'local' work, the greater height will give you quite a bit more 'line of sight' range-as long as the roof doesn't attenuate the signal. In both cases, you may have an issue talking with stations using vertical polarization- the cross polarization loss (assuming 11 meters) could be as much as 20-30 Db-which would be several 'S-units'. For other situations the greater height will lower the 'radiation angle' meaning more signal will hit the ionosphere at usable angles.

Hope this helps.
It does help. Thank you. The cross polarization thing is interesting. I never thought of that. Learn something new every day!
The roof attenuating the signal is something I'm not sure about. It's just regular asphalt shingles. But I think I recall reading that they can cause some signal loss.
 

jwt873

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You should get a decent signal out through the wood and shingles.

One thing to consider though, is the proximity of house wiring in the ceiling underneath and around the antenna. It could affect the tuning.

But even indoors, I think 20 feet would provide a big advantage over 5 feet.

If you need to use an attic antenna, another thing you might try is install a vertical mobile antenna up there. A full 108 inch quarter wave probably won't fit but there are shorter ones in the 4 - 5 foot range. You'd have to run wire radials around it for best performance. I don't know if it would outperform a dipole, but It's something I would try :)
 

jquittum

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Sorry. Saw this and thought I was in the right place.
"For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum."

So anyway, lets call it a 10 meter dipole.
 

WA8ZTZ

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Sorry. Saw this and thought I was in the right place.
"For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum."

So anyway, lets call it a 10 meter dipole.
Wasn't sure what you were trying to accomplish. If the antenna is for CB, a dipole is not he best choice regardless where it is located due to the polarization issue and the fact that it is somewhat directional.

Otherwise, for practical purposes, you probably won't notice any difference between an attic antenna and an outdoor antenna at the same height. However, if there is wiring in the attic nearby the antenna it could cause noise on receive.
 

jquittum

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I'd like to work 10 meters. I can get the antenna much higher, easier, in the attic, than I can outdoors right now.
 

TheSpaceMann

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Can you put an A-99 or a ground plane up outdoors? They would work well on both 10 and 11 meters!
 

jquittum

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I've been thinking about an A99. I might pick one up next weekend and try it out.
 

TheSpaceMann

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How high do you have it up?
I actually had it mounted to a back deck! The mast was not more than 10 feet, so the tip of the antenna just partially cleared the roof of the home. Still, I got out really well, especially when the skip was rolling in! :)
 

jquittum

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I actually had it mounted to a back deck! The mast was not more than 10 feet, so the tip of the antenna just partially cleared the roof of the home. Still, I got out really well, especially when the skip was rolling in! :)
Good to Know! Thank you.
 

SCPD

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I don't think an antenna mounted inside an attic, or out side, a few feet above the ridge line, will preform any differently. 5 feet above the ground, outside? I would put it outside, for another reason (below) but both should work about equal for DX skip. As the others have said, electrical wiring in the attic can effect it, and maybe things like aluminum backed insulation, if its up there.... is there metal flashing along the roof line?... and so on. Probably the best indications as to what the antenna is doing is your SWR... at least to see how well it resonates in that environment... but it will not say anything about its radiation properties (polarization etc.)
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Operating from an antenna in an attic just doesn't seem to be quite real Ham Radio though, does it?...Sort of like you're a clandestine spy station-- If so, I know; I have felt the same way doing exactly the same thing....... well, just think of the roof as a great radome- with no worries about the snows, winds or the neighborhood HOA's.
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.... Sounds like you have the makings of an interesting antenna experiment... :)
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.......................................CF
 
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jquittum

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I think I'll try it just because it's already made. Just have to crawl up there and do it. Will wait for it to warm up a bit. It's 4 degrees here now and the attic is not much warmer.
 

SCPD

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When the weather gets warmer, JQ, why not try them both? A coax switch to select one v.s the other in quick time with actual signals- I'm sure it would provide some interesting results.
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I don't envy your climbing about in a freezing attic- the fiberglass insulation itch's nasty, No?... :)
Ah, but its all in the name of science !
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............................................CF
 

jquittum

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Well, the dipole in the attic didn't work well at all. My discone antenna 20 feet up outside works much better, but still only receiving clearly on ssb from 20 miles maybe, and not getting out that far on tx.
Next is the Imax mounted on the same mast as the discone I think. Warming up to near fourty into next weekend, so we'll shoot for getting it up then. I was going to try a Sirio Gain Master, but, read that it is fairly narrow banded and doesn't like being near any other antennas.
 

SCPD

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Hmmmm... that doesn't come as a surprise. While the attic antenna may show all the signs of working superbly (SWR etc) - so would a dummy load. It's anyone's guess what the effects of the close-in environment of that 'radome' are upon the radiation patterns of your dipole. I can tell you there is a whole science to radomes (oh, and do I have stories!) I wouldn't discount it until you have tried it on skip signals, however. It is my guess it is has a very high angle of mixed polarized radiation- not at all good for nearby stations (as evidenced by your other antenna.)
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If I were facing this as a scientific issue, I'd first want a standard I could compare my design antennas against. I'd put up a simple quarter wave vertical- as in the clear as possible, at least a half wavelength high.... perfect SWR with no tuners, 50 Ohm cable direct fed, with quarter wave radials sloping ~45 degrees.... so on. Against this I would evaluate the other exotics. Also my guess would be that this Standard Antenna might be "The" one to use when all the dust settles.
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It starts to get fun, doesn't it?..... :)
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....................CF
 
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TheSpaceMann

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Well, the dipole in the attic didn't work well at all. My discone antenna 20 feet up outside works much better, but still only receiving clearly on ssb from 20 miles maybe, and not getting out that far on tx.
Next is the Imax mounted on the same mast as the discone I think. Warming up to near fourty into next weekend, so we'll shoot for getting it up then. I was going to try a Sirio Gain Master, but, read that it is fairly narrow banded and doesn't like being near any other antennas.
That Imax 2000 is a fairly good antenna! You will be able to use it on several bands with a tuner.
 
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