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Author Topic: Using roof effectively  (Read 412 times)
K3IMW
Member

Posts: 80




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« on: March 22, 2002, 12:57:23 PM »

Living in an antenna-restricted neighborhood, I elieve I can get away with wire that physically lies on the roof (thin concrete tiles over wood and felt).  I want to work 10m through 40m.  My alternatives seem to be:

  - 53' dipole on the ridgeline of the roof (at about 30')
  - 50'x25' loop around the edge of the roof (at about 25')

In either case I'll be using ladder line to a tuner in the shack.

Loop+ladder seems to be the current preference, but I wonder whether the additional height of the
dipole and its distance from the concrete tiles will outweigh the advantage of the loop?  Anyone tried both
approaches?

73 de ian k3imw/6



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WB2WIK
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Posts: 20536




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« Reply #1 on: March 22, 2002, 01:15:01 PM »

I'd go for the loop.  It is far less likely to be detuned by the proximity of the cement tiles than a doublet would be.  Also, the tiles you refer to, unless you've got something very unusual there, are normally called "lightweight cement," and they are very non-conductive.  My last house had such tiles -- about 4,800 of them! -- and a few broke during the '94 Northridge earthquake, driving me to investigate their properties in detail as I was doing the repairs.

I'd definitely use well insulated wire, and go the loop route.  And if you can avoid walking on the tiles, I'd do that, too!  (They break fairly easily if not walked on very gently, in just the right places.)

73,

Steve, WB2WIK/6
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K3AN
Member

Posts: 787




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« Reply #2 on: March 22, 2002, 02:02:00 PM »

If your roof edge dimensions really are 50' x 25', then that's just slightly long for a full wave loop for 40 Meters (1004/f). After you put the wire up, you may find that just a little trimming will resonate the loop near the low end of 40, so it will also be resonant on 20, 15 and 10.

This length of loop may be hard to match on 80, but I think you will be pleased with its performance on 40 and up. Good luck with your installation, and have fun experimenting.  

73,
K3AN

P.S. Consider buying, or at least borrow, an SWR analyzer (I like the Autek RF-1). They are practically indispensible for antenna experimenters.
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W0FM
Member

Posts: 2052




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« Reply #3 on: March 22, 2002, 04:08:45 PM »

Hi Ian.  Looks like you've already gotten good answers to your question, so I'll just add a constructive tip.  When you get the loop tuned to the point that you are happy with it, tack the corners down with small dabs of silicone caulking.  Maybe add a few dabs every few feet along the lengths as well.  It will keep the wire in place in windy weather.  It's pretty easy to pop it off if you want to take the antenna up.  I used black wire and black silicone to tack it to my black roofing shingles.  Down right invisible!  Good luck and have fun.

Terry, WØFM
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KC7CRR
Member

Posts: 61




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« Reply #4 on: March 22, 2002, 04:35:01 PM »

Hello Ian,

I have been a using a 40 meter wire loop for several years now. It is called a "Droopy Loop" and lays directly on my roof. It is definitely a compromise antenna...but it does work (some folks call it a cloud warmer)! This is a truly a "stealth" antenna if you are in an area with cc&rs.
It is fed with 450 ohm ladder line and requires a tuner. So far, I have used it on all bands (10 -160m),except for 30m. It gets used mostly for checking in to a 75m evening net. I do have other antennas for the higher bands.
If you can, see article in June or July 1996 issue of QST. If not, I would be glad to make a copy and send it to you.
Good Luck!!

73s de KC7CRR
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K3IMW
Member

Posts: 80




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« Reply #5 on: March 22, 2002, 07:42:23 PM »

OK, the loop wins unanimously. Thanks for all the suggestions.  I'll adjust the dimensions for 40m, and look for black silicone caulking. I already have an antenna analyzer (indispensible, I agree).

Might get it installed this weekend, will report results if so.

Thanks all,

--ian k3imw/6
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KD5QPF
Member

Posts: 42




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« Reply #6 on: March 23, 2002, 10:01:39 AM »

Wow... talk about perfect timing. I have essentially the same limitations due to condo CC&R's and was considering the same approach (ridge dipole or perimeter loop) to improve my current attic based 'antenna farm'. I even have concrete roof tiles as well (so thanks all for the good tile info)!

So yes, please report your results.

Now if I could just figure out how to get up to the 2nd story roof (no 20'+ ladder here) and/or not attract attention to exactly what I'm doing.

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K3IMW
Member

Posts: 80




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« Reply #7 on: March 23, 2002, 01:44:36 PM »

I forgot to reply to this message specifically:

>
> I have been a using a 40 meter wire loop for several years now. It is
called a "Droopy Loop" and lays directly on my roof. It is definitely a
compromise antenna...but it does work (some folks call it a cloud warmer)!
This is a truly a "stealth" antenna if you are in an area with cc&rs.
> It is fed with 450 ohm ladder line and requires a tuner. So far, I have
used it on all bands (10 -160m),except for 30m. It gets used mostly for
checking in to a 75m evening net. I do have other antennas for the higher
bands.
> If you can, see article in June or July 1996 issue of QST. If not, I would
be glad to make a copy and send it to you.

Yes, please!  I can find the reference but not the text.  My address is
correct at qrz.com.

Thanks,

--ian k3imw



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KD5QPF
Member

Posts: 42




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« Reply #8 on: March 24, 2002, 08:18:36 AM »

KC7CRR: If you would be so kind as to mail me a copy as well I definately would appreciate it. My address is correct on eHam (e.g. just look me up in the call sign database here).

Thanks & 73

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WB6BYU
Member

Posts: 12974




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« Reply #9 on: March 25, 2002, 11:24:59 AM »

I wouldn't worry about adjusting the loop dimensions for resonance
on 40m - that is only important if you are trying to use coax feed.
With ladder line, you need a tuner anyway, so just put up as big
as a wire loop as possible and tune it.  (Besides, making repeated
trips to the roof to tune it would attract unwanted attention to it.)

I have had good luck running the wire on the back side of the
facia boards around the outside of the roof.  It is out of the weather
and you don't have to walk on the shingles.  Unless you are going
to be running a lot of power, I suggest just stapling insulated wire
to the back of the boards.  If anyone asks, you can say you are
hanging Christmas lights, or installing a bat repeller so they don't
nest under the eaves.
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KC7CRR
Member

Posts: 61




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« Reply #10 on: March 26, 2002, 11:16:21 AM »

Ian,

The QST loop article will go out in tomorrow's mail.

KC7CRR
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KC7CRR
Member

Posts: 61




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« Reply #11 on: March 26, 2002, 11:18:20 AM »

Mike,

The QST loop article will go in tomorrow's mail.

KC7CRR
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