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Author Topic: Antenna on shingles questions  (Read 1825 times)
KB9MNM
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Posts: 17




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« on: June 05, 2011, 02:39:45 PM »

Would anyone know what kind of effect asphalt shingles would have on a wire antenna, if any? I was reading Winegard TV antenna's website and they state that with the shingles,felt and 3/4" sheathing, there is a 50% loss in signal reception for TV freqs.

I was thinking if my house's roof is blocking, or going to block, that much signal, I should get the dipole outside. I would like to make 2 antennas, one n/s one e/w and the other choice I have is to lay an antenna on the roof, hence my question.

Thanks and 73!
Dave
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W8JX
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« Reply #1 on: June 05, 2011, 02:50:22 PM »

Your roof does not provide much of a barrier to HF frequencies. Many have had good results with attic antennas.
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All posted wireless using Win 8.1 RT, a Android tablet using 4G/LTE/WiFi or Sprint Note 3.
KB9MNM
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Posts: 17




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« Reply #2 on: June 05, 2011, 03:40:00 PM »

Thanks for the reply!
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WB6BYU
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Posts: 13235




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« Reply #3 on: June 05, 2011, 05:29:23 PM »

Yes, many folks have had good results with attic antennas, and many have also noticed that it worked
much better when they got the antenna outside.

It is difficult to know, however, as there is so much variation in construction materials.  Even the composition
of composition shingles isn't a constant.

There are really two factors:  the losses of RF passing through the roof, and the losses when the wire is so
close to the shingles that the shingles form part of the dielectric.  This latter case applies, for example, if
the wire is right under the shingles, or if the wire is put on the roof and tucked under the ends of the
shingles.

I've done both in a variety of situations.  The wire under the shingles generally worked better, especially
with wood shingles (which have low dielectric losses when they are dry.)    Tucking the wire under
asphalt shingles will also change the resonant frequency:  for loop antennas on the roof I've found that
the standard formulas resonate about 10% to 20% lower than expected.

But if you are planning to put up two dipoles, then you have a wonderful opportunity to compare the
two and see how it works in your house.  Run the two antennas to a coax switch so you can toggle
between them quickly and see which one seems better more of the time.
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G8JNJ
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Posts: 492


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« Reply #4 on: June 06, 2011, 01:07:50 AM »

Hi Dave,

I'm also looking at alternative attic / roof antennas.

My experience is that if you can space the wire away from the shingles byat least 6" but even 1"  (electric fence insulators and standoffs are good for this) it makes a difference. It also reduces the fire risk at high voltage nodes if you are running power.

If you have space both N-S and E-W take a look at the

March 2011 QST -  A Four Wire Steerable V Beam

and

http://www.gb2nlo.org/index.php/x-ant

For some ideas about how to electrically steer fixed antennas.

Thin wires sloping down from a short (or long) insulated pole mounted on the roof to 10ft (or more) high posts or trees in the garden are one stealthy way to implement it.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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W5WSS
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Posts: 1724




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« Reply #5 on: June 06, 2011, 01:12:29 PM »

One could deploy an indoor horizontal oriented horizontal radiating square loop with knife switches installed at points about the perimeter for directional control or for feed point impedance management. What I attempted to do with the switches was to remove apx. 3ft of wire from each corner in essence an open loop steerable mechanically via hand throwing open or close the respective corners. A wide range tuner is required preferably at the feed point. I used a four sided square I called the crippled loop to form cardioid patterns in four separate directions that overlapped slightly around the compass for complete worldwide coverage. The switching was crude and slow but was an interesting endeavor. One knife switch across the way from the feed point was useful too. Modeling revealed promising results but empiricism won out due to proximity issues from the indoor environment mutual coupling of many active conductors. Anyway was alot of worthwhile time having fun learning. 73
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KE3WH
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« Reply #6 on: June 08, 2011, 05:29:39 AM »

Strange thing about roof and attic antennas, the installations you look at and say they cant possibly work, do.
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First ticket 1980. Ex KA3EWT, N3DSO.
W0FM
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Posts: 2055




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« Reply #7 on: June 08, 2011, 11:15:16 AM »

I have dipoles and yagis in my attic which has asphalt shingles, felt paper and plywood above it.  I have also used wire laid directly on the asphalt shingles and tacked down with little dabs of silicon caulk.  Neither were as good as a dipole high in the clear outside, but both worked and I had fun.  Be sure to apply a liberal amount of common sense when planning your installation.

DX confirmed is over 236 with the attic dipoles.

73,

Terry, WØFM
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