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Author Topic: Attic antenna advise  (Read 15585 times)
N9MGO
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« Reply #15 on: September 05, 2017, 12:59:16 PM »

Thanks, this is the kind of advice I'm looking for.
Mike
N9MGO
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AE0Q
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« Reply #16 on: September 05, 2017, 06:56:29 PM »

FYI: I have two fan dipoles in my attic (one for 40/20/10m with 40m being physically short with coils, and one for 17m/12m). They are center fed dipoles with current baluns at the feed points. According to my MFJ-854 (of questionable quality and performance), there is still some amount of (what I assume to be common mode) current on the coax outer and also various AC power cords around the shack. I can't determine whether it's common mode as a 3rd current path coming down the coax outer somehow getting past the current balun, or whether the near field is inducing current on any conductor in the vicinity, since my antennas are so close to the operating position. I'm also not sure what level of CM current is normal and acceptable or whether that number needs to be 0 (or at least not measureable to any degree). I might need to start a separate post to get some opinions on that. I guess my point is that for attic antennas, it might be advisable to avoid antennas that are known for CM current, such as OCF and end-fed types and to try to isolate the feed line with a good current balun to at least minimize whatever CM current might be produced.

I agree with the above advice, make the antenna a fan dipole.  I put one in my attic with legs made from lengths of 300 ohm ribbon TV twinlead.  I made the longest a full size 40m dipole, and then peeled back the second wire of that piece to make a 30m dipole.  The 2nd was cut for 20m and 10m.  The ends of the 40m section were bent at each end to fit the attic.  All 4 wires on each side were tied together.  The whole thing was fed with foam twinlead and that ran into the room below where I used an L-match antenna tuner.  The dipole legs were stapled to the roof joists at the highest points possible.  I used that setup for 16 years, have since moved to a different location with no access to an attic so I have each half of a 40m dipole winding around an outside porch on each side of the house.

Glenn AE0Q
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Glenn and V-NATCH Katie,
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http://www.hoopsandjumps.com/
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N9MGO
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« Reply #17 on: September 06, 2017, 08:40:50 AM »

Glenn,
I really like that idea, I think I understand what you are describing.  I am trying to visualize it and how I could adapt it to my attic.  Just by chance, if you had a pic of your set up that would be helpful.  My attic is about 30' wide at the peak and slopes down to the front and back side of the house, that run is about just over 40', but very hard to access as the ceiling closes down.  The attic has the framework spaced 24" apart and has blown in insulation.
Mike
M9MGO
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KL7CW
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« Reply #18 on: September 06, 2017, 10:04:03 AM »

I have an idea you could try for the legs of the dipole which slope down into the insulation.  Put an endcap on a piece of PVC (only costs about $2 for a 10 foot length). Push the capped end down into the insulation as far as possible and slope the top end up toward the peak of the roof.  You could attach the PVC to the rafter, or mount it on some standoff insulators.  Snake a wire down into the PVC as far as you want to go....you may want to have the wire end a bit above the attic floor.  Attach this wire to the ridge dipole.  If you need to adjust the antenna length a bit, you could simply pull the wire up a bit and re solder it, or better use a connector to shift the length a bit if the antenna will not tune on a particular band of interest.  If you need a slightly longer antenna for something like 40 or 80 meters, you could use something like an electrical 1/2 inch PVC gradual 90 degree conduit sweep instead of an end cap and and extend the attic floor end back along the attic floor possibly something like 5 or 10 feet if you really need the extra wire. Antennas which utilize a folded back design can have nearly full size performance IF:  A) the folded back portion is not too close to the other wire.  B) if the folded back portion is somewhat shorter than the other wire.  For example the Steppir dipoles with folded back 40 meter elements have performance very close to a full size dipole (< one dB I think).  The folded back portion is not close to the outgoing wire and the wire inside the tube does not go all the way back to the center.  Now this approach might "screw up" your pattern on higher frequencies, so this is just something to consider. If you use insulated wire (perhaps something like inexpensive #14 solid house wire, especially if in PVC tubes, the wire will act like it is something like it is several percent longer due to the insulation.  I suspect you could push it into the conduit OK, unless the run is long, or you use a sharp 90 degree elbow at the end.  I was going to install PVC conduit into an attic for a senior citizen with the center portion right above the attic access hatch.  The idea was that he could stand on a short step ladder and snake wires of various lengths into the conduit and experiment all he wanted without climbing into the attic.  He moved or died before we could try the idea. 
            Rick  KL7CW
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N9MGO
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Posts: 24




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« Reply #19 on: September 06, 2017, 03:11:10 PM »

That sounds like an interesting solution.
Mike
N9MGO
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N9MGO
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Posts: 24




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« Reply #20 on: September 06, 2017, 05:14:03 PM »

I also found EAntennas makes an interesting fan dipole which may work well for this application.  Does anyone have any experience with this brand as used in an attic?
Mike
N9MGO
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KD8NGE
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« Reply #21 on: September 09, 2017, 04:12:00 PM »

 Grin As usual, more than the OP benefit from the several replies!
I too am VERY interested in the attic as my antenna farm!
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K4FMH
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« Reply #22 on: September 26, 2017, 07:53:43 AM »

Just another set of observations on my own attic antenna farm...

I use a Ventenna dual-bander for 2M/70cm and it's about 40' above ground on my two-story house. Works very well for my area. On HF, I have a sort-of horizontal loop inserted just UNDER the outer lip of the roof shingles with the ends entering my large attic at a soffit point to connect to a balun. I have an MFJ 80/40 dipole strung mostly at the ridge peak but tapering down at the ends. I'm hanging a Radiowavz 4-band (20-17-15-10) fan dipole later this week off to the side of the ridge peak (not directly under the 80/40 dipole) off-set from the joists using plastic fence posts (from Tractor Supply). I also have two dipoles, one for 20M and another for 15M, installed as inverted Vee's along the joists. This gives my azimuthal bearings a right-angle coverage on 20/15 to the others...which point broadside directly to Europe. The 20/15 inverted Vee's point toward Asia and Brazil/South Africa. Not much DX to report given the band Cx but the meter readings on SWR and Nx work ok for attic installs. I also have an MFJ Rx Loop in the attic on a small rotator as a receive antenna when needed on the lower bands.

Hope this helps with ideas!

73,

Frank
K4FMH

PS: I too have the foil backed radiator roof material....can't say it hurts a bit. See the eHam article on this topic.
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W3ALG
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Posts: 26




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« Reply #23 on: September 27, 2017, 06:29:08 AM »

I am lucky to have a huge 2200 sq ft.attic. My air conditioning duct runs up through the center which leaves the outer perimeter open. I use a Buckmaster  80-6 meter dipole antenna which spans 135ft. I have this around the inside using fence insulators from Tractor Supply that I have positioned on every other stud. Another antenna is a Radio Oasis G5RV Multi band 40-10m which I have positioned North & South. (51ft)  One more antenna I have for 2m / 440 operation is a Diamond X50 Vertical. I live in an HOA and all my QSO's are run from these antennas. I have worked close to 100 countries running 100 watts! Its astounding that a lot of times I break through pileups on my first call.

Nothing is fancy with these setups. My coax cables are run from the attic to the lower level of the house,75ft into my den/shack. I have enough cable that I can position the radios where ever I want. I power 4 radios and use a Diawa antenna switch.

One thing to pass along. I had absolutely NO ONE to show me anything when I got into ham radio and just studied and read articles about the hobby. I decided to dive into it and was totally blind and didn't know if any of this would work. Needless to say, it did! I'm fortunate to have a big attic and maybe it's the location, but I'm not on a mountaintop.

My advice is to try anything and see what works in your situation. You may be surprised at the results. Its part of the fun and the hobby.     
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N9MGO
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« Reply #24 on: September 28, 2017, 08:36:28 AM »

Thanks for the current info, it all helps.  I am currently on hold as I want to get as much info as possible, so this is all helpful.  As I mentioned earlier, I have an Ed Fong dual band that will be jutting up somewhere in the attic for 2M/440 and maybe an old mag mount scanner antenna in a cookie sheet for some scanner stuff.  When it comes to the HF, I'm all ears(pun intended), I figure the more research the better, just like measure twice and cut once.
Thanks,
Mike
N9MGO
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ONAIR
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« Reply #25 on: September 28, 2017, 11:57:08 AM »

I've had excellent results using a small ELK vhf/uhf beam inside an attic!
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KC4ZGP
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« Reply #26 on: September 29, 2017, 05:53:34 AM »



All those nails holding down the shingles. Hmmm...

Kraus
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KC1BMD
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Posts: 612




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« Reply #27 on: October 06, 2017, 04:41:50 AM »

In my earlier post, I forgot to mention that I have two fan dipoles in my attic (40-shortened/20/10m and 17/12m slightly inverted-V's, maybe 22-24' high, Flex Weave insulated 14ga wire, current baluns and RG8x feed lines to 2nd floor shack). It's a townhouse condo and I only have attic access through a ceiling panel in a 2nd floor bedroom closet. I have to walk on the floor joists carefully so I don't punch a hole through a ceiling below. It's all trusses, 24" on center and difficult to get around. Nevertheless, I got them installed and other than the occasional CO detector tripping (that I wish I could solve but have not been successful) I am able to work all states and lots of DX on 100W (often less). It's certainly not optimal but it gets me out. I certainly appreciate people with the big towers and high power that do a lot of the heavy lifting to make my QSO's successful. Sometimes I can work other low power stations when band conditions cooperate. Lots of luck and let us know the results!
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KC4ZGP
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« Reply #28 on: October 06, 2017, 05:45:27 AM »


I'd say work all states and lots of DX on a hundred watts is quite optimal.

I talked to one gent, SSB phone. His antenna 70 feet up, 700 watts. He sounded like
you or I as you put it 'less than optimal' at one-hundred watts.

Press on with your attic adventures. You're having more fun than the aforementioned
gentleman.

Kraus

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KC1BMD
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« Reply #29 on: October 06, 2017, 06:16:20 AM »

You're having more fun than the aforementioned gentleman.

If I'm the "aforementioned gentleman", well, I'm having lots of fun! (except for the difficult attic access Smiley). To be clear, I'm not saying to not install an attic antenna... mine has proven to work.
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