Elecraft

Attic Antenna

Classic

List

Threaded

4 messages Options

KB5DXY

Attic Antenna

Ron D'Eau Claire-2

RE: Attic Antenna

I live in a restricted community and am thinking about putting a 20
meter dipole in the attic. I know most of the issues with doing this but
I don't know the effect the roofing material will have on my signal. The
roof is 1/2 in thick cement tiles. Has anyone had experience with this
setup?

Thanks,

Larry, KB5DXY
K1 #2269

---------------------------

Yep! Not all tiles are equal, so you may be better off. I moved several
times about 15 years ago, always living in an apartment. I managed to get a
top (second) floor apartment in each case and installed a doublet in the
attic in each case. It was hung just under the rafters.

In one apartment I noticed that I didn't get out very well, compared to my
previous QTH, but my antenna arrangement was very similar! On air testing is
just about useless to determine how well an antenna is working so I didn't
panic over it. But, over several months a suspicion grew.

One day I noticed walk near my building a piece of roofing tile that had
apparently dropped there while some repairs were being done. Curious, I took
it indoors. It was a hot summer day and the tile piece was quite dry. I put
it in my microwave oven (with a glass of water to avoid running it 'empty')
let it cook for a minute or two.

The roof tile was very hot! That's a sure sign it's pretty opaque to RF. Of
course, it's probably more opaque at microwave frequencies than at HF, but
it's still going to be lossy. If you can get a piece of tile, do the test
for yourself. You may be a lot better off than I was.

I did a little research and found that those tile mixes often have a lot of
stuff not normally found in concrete and that the formulas vary
substantially from one supplier to another. That's about all I could dig up
on the subject. Let me say that I made a LOT of contacts from under those
tiles, using QRP on 40 and 20 meters, including substantial DX. That's the
problem with on-air testing. A punk poor antenna can sound *great* when the
band conditions are right. So if that's what you have to do to get on the
air, go for it.

Ron AC7AC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Rick Dettinger-2

Re: Attic Antenna

In reply to this post by KB5DXY

> I live in a restricted community and am thinking about putting a 20
> meter dipole in the attic. I know most of the issues with doing this but
> I don't know the effect the roofing material will have on my signal. The
> roof is 1/2 in thick cement tiles. Has anyone had experience with this
> setup?
>
> Thanks,
>
> Larry, KB5DXY
> K1 #2269

=========================================
The attenuation of any materal is a function of its thickness, measured in
wavelengths, as well as its electrical properties. This means that for a
given roof material, you will have less signal attenuation at 160 M then at
10 M. This should be true for trees, rain or snow also. This is why the US
Navy uses extreme low frequencies to communicate with subs under water.
Like in the audio range, except its still radio.
I tried a 20 M. dipole in my wood framed attic before I hade an antenna
tuner. The SWR was way high, like 4:1. I think this was due to the close
proximity of electrical wires. The antenna would probably have worked fine
with a tuner.
Rick Dettinger
K7MW

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

KB5DXY

Re: Attic Antenna

Thanks for all of the great feedback. I am going to research some of the
antenna suggestions that I have received. I feel a lot more confident in
trying an antenna in the attic now.

I am currently building my K1. I have finished the receiver and am
starting the transmitter section. I will also be adding a KAT1. I will
report back with results when I get the whole thing working.

Larry, KB5DXY
K1 #2269 (in progress)
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com