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Author Topic: Antenna location, Indoor or Out  (Read 1194 times)
N0FI
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Posts: 14




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« on: December 05, 2002, 09:28:02 AM »

I recently have been playing around building Homebrew VHF and UHF antennas, as I am far enough in the country where I can't always hit the repeaters with an HT.

Here is the problem. I am trying to determine the best place to put the antennas. I live in an old 2 story house with a big attic.  If I mount them In the attic, they will be slightly lower (less than 10 ft) but shielded from the weather, more accessable (I can access them easily at any time, any weather) and have a shorter (20-30') feed line. If I mount them on the roof, it will be hard to access (I live MN, and am not going on an icy roof).

How much loss can I expect from having the antennas in the attic? I have been looking around, but have found nothing that addresses this issue. I will be putting up a tower in a few years, but in the mean time, want to make the most of what I have.

Thanks,
Matt Carlson   N0FI
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WB2WIK
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Posts: 20611




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« Reply #1 on: December 05, 2002, 02:54:05 PM »

I'd put them "topside," up on the roof.  You shouldn't have to access antennas once they're installed, unless they get hit by an eagle or struck by lightning or some other rare catastrophe.  I've installed VHF-UHF antennas on roofs and then never looked at them again, ever, until I moved.  They should last many years without fuss.

It's impossible to estimate the loss you'll encounter with indoor, attic-installed antennas because this will be dependant upon so many variables, including:

-Siding material
-Presence of insulation, and if so, what kind
-Wiring and plumbing in or near the attic
-Roofing material

In most "modern" homes, unless "engineered for indoor antennas" (which can be done, especially if you have a custom-built home), the attic is a sinky place for antennas because:

-Foil-lined bat insulation is very popular and creates horrendous losses
-Stucco siding is also very popular and is also very lossy for RF (a lot of that is because of the wire lathe used to hold the stucco in place)
-Some roofing (shingle) materials are horrendous dielectrics for RF
-And, maybe most importantly, it's common for telephone, CATV, alarm system, electric utility and other wiring to run through attics, making them very prone to interference.

Most, if not all, of these problems are elminated by simply placing the antennas above the roofs, and outside.

With an older home, an indoor antenna might work better, especially if you don't have all the wiring, insulation etc. up there.

In the case of one home I owned, of 20 year-old conventional construction, I installed a Hustler G6 2m omni FM antenna in the attic temporarily as the roofing was being replaced...the difference between "inside" and "outside" (same feedline, difference in overall height maybe 10 feet) was rather staggering.  With the antenna on a mast on the roof, I could easily access (full quieting) a repeater in the Mojave area, 75 miles away.  Same antenna indoors (with the same feedline, just pulled through an attic vent) could barely hear the same repeater, let alone access it.  My offhand guess would be the difference in performance, in most directions, was 20 dB.

Although, as usual, had I not had data for comparison, I never would have known that!  With the antenna indoors, it still worked, and made lots of contacts.  Just all those contacts were closer...

WB2WIK/6
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N0FI
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Posts: 14




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« Reply #2 on: December 05, 2002, 03:28:51 PM »

Thanks WB2WIK,

For a little more background, the house is 100 years, old, there is no insulation (it is in the floor below the antenna) no wiring, vinal siding. All good points that I hadn't thought of mentioning. It still has very thick rough cut lumber and shingles (maybe even 2 layers). And of course, wiring in the floor below could cause some interference.

It is common in this part of the world (MN) to put your TV antennas in the attic, but I am willing to bet there is a lot bigger sacrifice than most people realize.

The loss you experienced is enough to convince me to brave the cold and put it on the roof.

thanks-
Matt Carlson  N0FI
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KB0NLY
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Posts: 1




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« Reply #3 on: December 05, 2002, 08:45:22 PM »

Being in Minnesota myself i would like to offer some advice on a cheap "tower" installation.

My primary antenna support is a wooden utility pole, i got a used one from the local power cooperative.  The best thing to do is get one longer than you need.  For example i have aproximately 40 feet of pole and mast above the surface of the ground, but you have to figure for at least 5-6 feet of the pole being in the ground, and you want to have the extra length available to cut off the top part that is normally full of holes from the cross braces and insulators etc. and to be able to clean up the bottom of the pole if it has any rot.  But of course the best thing is to find one without any sign of rot to begin with, the best choice is one that has been treated with tar to water proof the part in the ground.

Anyway, my setup is simple, cheap, effective, and best of all eay to maintain.  I have a mast hinged to one side of the utility pole which is raised and lowered with a winch on the opposite side, the cable goes up to near the top, through a pulley, and attaches to the mast.  If you have a good winch which allows to lock it in place you don't need a latch or something similar to safely secure the mast once winched up.  Im my case i mounted a spring loaded latch to the pole and welded the matching piece to the mast, it is unlatched from the ground by pulling on a rope attached to it.  When the mast is winched up it simply latches itself in place.

73,

Scott, KBØNLY

www.qsl.net/kb0nly

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WB2WIK
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Posts: 20611




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« Reply #4 on: December 06, 2002, 01:10:40 PM »

N0FI: I love 100 year-old houses!  For me, the older, the better -- for the charm, smell and feel of a house.  But be careful, as it may have a 100 year-old roof, too.  Wouldn't want to hear about you falling through it.

I had a very old home once, with an original slate roof.  Nice to look at, almost impossible to walk on.

Safety first, and wait for a warmer day!  I heard it was 12 degrees in St. Paul this morning...

73,

Steve WB2WIK/6
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K5DVW
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Posts: 2193




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« Reply #5 on: January 13, 2003, 12:24:53 PM »

I live in a restricted community, antenna restricted that is.... I have to put my VHF stuff in the attic.

I have three beams. 6m, 144, 440 all on one mast which is on a tripod and has a cheap rotator. Works well for me. I have a huge attic and it all fits.
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K1RDD
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Posts: 213


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« Reply #6 on: January 22, 2003, 09:40:39 AM »

My attic currently has a 440/2m mag mount on a 4' x 4' piece of sheet metal. For HF, I have a single feed point 10/15/20m dipole. From MA, I have worked as far as Russia, Argentina and British Columbia. The only antenna I can't get to work inside is a trapped 80m dipole.
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