Attic loss? - Elmers Forum at eHam.net

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eHam.net Forum : Elmers : Attic loss?

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Attic loss?	Reply
by K0OOK on February 3, 2003	Mail this to a friend!
Hi! I looks like I've got a nice attic above the garage that's got around 12 - 15 feet of room. It looks like enough to put in a small 6m or 2m beam. I've been thinking about doing some sideband on those bands and was wondering if there's going to be much loss going through a wood and shingle roof? I'll be running 100 watts on 6m and 50 watts on 2m. Thanks! Pat

RE: Attic loss?	Reply
by K5LXP on February 3, 2003	Mail this to a friend!
There's always some interaction to the structure when installing antennas indoors. The roof itself may be wood but there is 120V wiring, pipes, vent shafts, metal flashing under the shingles, etc that will all affect an antenna's performance. There's no way to really predict what it will do until you try it, but don't be suprised if the SWR is a little high, and at the power levels you propose (esp. 6M) you may have some RFI problems in the house. I've read enough success stories about indoor antennas that I would try it if there were no other option, but I've also read enough tales of woe about indoor antennas not to be too disappointed if it doesn't work. Mark K5LXP Albuquerque, NM k5lxp@arrl.net

RE: Attic loss?	Reply
by KT8K on February 3, 2003	Mail this to a friend!
Wood shouldn't attenuate RF much, nor shingles unless they have a lot of metallic content. Ridge vent screens may be metal, and any metal siding or other nearby metal may detune your antenna or parasitically absorb some of your signal. In the absence of metallic objects your signal should get out of the attic quite well. Good luck & hope to C U on the bands. 73 de kt8k - Tim

RE: Attic loss?	Reply
by K1RDD on February 3, 2003	Mail this to a friend!
You never know until you try. In my attic, I have a 2m whip/magmount on a 4' x 4' piece of sheetmetal. I am often told that I have one of the strongest signals into the repeaters, as well as simplex. In addition, I have a 10/15/20m wire dipole which I have worked as far away as Russia, Argentina and British Columbia from MA, with consistant 559 reports on CW and 58 on phone. On the other hand, I can't get 80 to work to save my life. I am using an IC706MKIIG.

RE: Attic loss?	Reply
by WB2WIK on February 3, 2003	Mail this to a friend!
As others have said, you never know until you try. But even then, you still won't know. Reason: Unless you try the beam in the attic and make measurements, and then try it outside of the attic and repeat those measurements, you'll have no idea how much you might be "losing" with the attic installation. I'll never forget my first such experiment, as a kid of 13 years, living in my parents' all-wood construction home (asphalt shingles, all wood construction otherwise). It was a 2-1/2 story split-level, with an attic about 20' above ground (at the attic floor), and I had a 2 meter ground plane antenna installed on a 5' mast in the attic. It worked "great." Then, several months later I had the opportunity to take the same antenna and mount it outside, on the chimney, only about five feet higher but now completely outdoors. Same coax, same antenna, even the same mast. The difference was astonishing. Several friends I had made on the air in towns about 15-20-25 miles away were used to hearing me with the "attic" ground plane, and quite strongly. Then, with the same "outdoor" antenna, the same friends couldn't even believe it was me. My signal had improved from "S9" to "fully pinning" their meters, a staggering difference. And now, with the antenna outdoors, I made new friends, 75-85-90 miles away, who I never heard before. Quite a lesson. WB2WIK/6

RE: Attic loss?	Reply
by W0FM on February 3, 2003	Mail this to a friend!
Aside from a Hustler 6BTV hidden among the trees out back, the remainder of my antennas are in the attic. I have confirmed 219 countries with a DX-EE dipole in the attic. In addition to the DX-EE, my attic "antenna farm" includes: Half wave dipoles for 12, 17 and 30M. Two discones. A 3 element 6M yagi. A pair of stacked halos for 6M. A 10M ground plane. Eggbeaters for 2M and 440. A 6M dipole, and my AO-40 satellite setup which is a 440 yagi and a 2.4 GHz BBQ grill dish. All "work well" and keep me active on the bands. Would I prefer to have them all at the top of a 100 ft tower? You bet! Bottom line. Attic antennas work with some obvious trade-offs. Use what you can and have fun. Terry, WØFM

RE: Attic loss?	Reply
by K6AER on February 4, 2003	Mail this to a friend!
Attic losses depend on the frequency and the type of material used in the roof construction. At 146 MHz roof losses can be as high as 20 dB for tile roof, 8 dB for asphalt shingle and as low as 5 dB for wood shake. Interaction with wiring layed along the floor of the attic will also alter the efficiency of your radiation paten. As WB2WIK said the best way is to do a comparison with an antenna outside and inside the attic. Good Luck. Mike - K6AER

RE: Attic loss?	Reply
by WB4OFM on March 13, 2003	Mail this to a friend!
Hello Everyone, I am going through the attic or not attic delima right now. We have a new house in central tn with massive (wasted for anyone but a ham) attic space. I was hoping to put all my vhf/uhf stuff up there and maybe some higher freq hf. After getting my workman dual band antenna up there as high as I could, I was pretty disappointed at the swr and its performance. I haven't given up on it just yet. I had it very close to the roof line and near the ac duct. So I will try it more in the middle of the structure although that will mean more feedline. I mounted a home made 1/4 wave for 2m up there also and it is great. I put it up just for my old midland 13-505 that stays on 1 repeater all the time and it recieves and radiates well. After reading this thread, I am wondering if I shouldn't just head for the outdoors with the dual band. Jim

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