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HF/VHF/UHF attic antenna options for 30'x25' attic?

Discussion in 'General Technical Questions and Answers' started by Pushraft, Oct 23, 2008.

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  1. Pushraft

    Pushraft Banned

    I am considering getting my ticket and want to know what attic antenna options I have. I measured the attic and got 30x25 feet with various heights from near 0 feet to about 10 feet max. I see a pair of those metal vertical ducts up there. One has about 10 feet visible and the other has maybe 7 or 8 feet visible. The base of the attic is about 28 feet above ground with a clear shot outside to the SW, W, and NW but some obstructions in the other directions. The terrain here is also very flat. The highest part of the attic is 38 feet above ground.

    1st question: What would be the easiest HF antenna to erect and amateur band to listen in on? The built in tuner on the Yaesu FT-767GX will only handle mismatched antennas of about 3:1 SWR according to the operator's manual so I dont want to "stress it out".

    2nd question: how would I be able to use multiple bands with just a single antenna or would I need multiple antennas up there?

    3rd question: Since I already have a Yagi-Uda antenna that will work with 70cm, would I be better off selling the Yaesu FT-767GX all band HF transceiver and getting say a 70cm HT and hitting one of the local repeaters? At least that way I will get some directivity.

    4th question: I also have a discone antenna which is supposed to be able to cover 27-900 Mhz maybe and is supposed to be able to Tx on several of those frequencies too but I forget which ones. Maybe I could use that as a generic 70cm, 2m, and 6m attic antenna. It will fit in the section of the attic that is about 10 feet tall but unfortunately that is where that 10 foot metal duct is nearby.

    5th question: I have 10 meter vertical end fed 1/2 wave antenna but I would have to mount in horizontally up there. Would that antenna only be good for 10m or can it be used for other bands too such as 12m, 15m, and even 20m?

    Remember I could just listen in on these bands to hear how far I am pulling in signals from so that is about 1/2 the fun. It would also motivate me more to get my ticket because if I hear people I would naturally want to try to talk back to them.
     
  2. WA4ILH

    WA4ILH Subscriber QRZ Page

    The simplest HF antenna is the center fed dipole. I have traditionally used center fed dipoles for the lower frequency bands. The theoretical impedance of a center fed, half wave antenna is about 72 ohms. Most radios will match this just fine. Also, you may be able to find some RG-6 TV type cable cheap which will work well here. To calculate the length of a half wave antenna in feet, divide 468 by the frequency. You can just fit a half wave 20 meter antenna in your attic (33.4 feet) and all of the higher frequency bands as well. (17,15,12 & 10 meters) You can attach any or all of these wires to the same feed point.
    Discone antennas are popular because they have very wide bandwidths. (the military loves them for this reason) They can even have some gain on some frequencies but I wouldn't guarantee that they would have gain on the frequencies that you're interested in. You can build "J" poles pretty cheap which will give you much more gain, and probably less noise (S/N). Good luck.
    Tom WA4ILH
     
  3. G4ILO

    G4ILO Ham Member QRZ Page

    The easiest attic HF antenna giving you coverage of all (or most) amateur bands is a loop of wire round the perimeter, fed with a remote SGC autocoupler in the center, which will match the wide range of loads presented by the loop on all bands to the 50-ohm coax used for the feeder. You can get battery operated models now that can be installed remotely.

    If you insist on using a limited range ATU in the transceiver, then you are restricted to resonant antennas which will make your work a lot harder. You can install a "fan dipole" for the main higher amateur bands. You can have up to 4 dipole elements, each for a different band, connected to a common center, and spread out at the ends.

    Coverage of the lower bands is problematic in any attic, though yours is larger than mine, and it should be possible to get decent results as long as you do not have a lot of metal up there to cause problems.

    Currently I am using a loaded multiband dipole for 80/40/20 plus an MFJ magnetic loop covering 40-15m. I plan to try "fanning" dipole elements for 10m and 6m to the multibander.

    My article on Stealth Amateur Radio has a lot of ideas based on personal experience of operating without outside antennas.
     
  4. W0IS

    W0IS Ham Member QRZ Page

    Here's my personal recommendation. Keep in mind that I've only been a ham for 35 years, so there might be a lot of flaws with this plan. But this is what I would do, based upon my personal experience over that short period of time.

    I would put up fanned dipoles for 40, 20, and 10 meters, which would also work well on 15 and 6 meters.

    You have 32.5 feet from the center of one side to the corner on the other side. This is almost long enough to reach a full-size 40 meter element. You can get a few extra feet by letting the wire droop a little bit, and by letting it go from the top of the roof to the floor of the attic on the opposite side.

    Run a piece of coax to the peak of the roof. From that point, you will also run 6 wires to the other side of the attic. There will be two of each, measuring 32.5, 16.5, and 8.3 feet. Hook one of each wire to the center connector of the coax, and one of each to the braid of the coax.

    Run these wires away from that point, as symmetrical as possible, and at as large an angle to each other as possible. The long ones will go to the opposite corners. The shorter ones will go to any convenient tie off point.

    Use any convenient insulated wire. Take care to not have the wires touch combustible ojbects.

    The 40 meter elements will be at a fairly sharp angle of 44 degrees, so the directional pattern might be difficult to predict. But in general, this antenna will work quite well on 40, 20, 15, 10, and 6.
     
  5. AI3V

    AI3V Ham Member QRZ Page

    This should do the trick:
     
  6. W0IS

    W0IS Ham Member QRZ Page

    I've worked people running that kind of antenna. It doesn't exhibit a lot of gain, but the SWR is always great.
     
  7. WB3BEL

    WB3BEL Ham Member QRZ Page

    Easiest antenna for receiving = any old random length wire in the attic. Just do it.

    When you get your license and want to transmit or get more interested in some specific band. Build a dipole fed with coax. 40 or 20 meters would be good bets at this point in the sunspot cycle. If you want multiple bands then use a fan dipole.

    You can easily build antennas that fit in the attic for 80m and higher frequencies. You could also build an antenna for 160m but it would not be a great performer. You could make contacts out to a few hundred miles maybe more if you were determined. Folks have made international DX contacts with mobile antennas on 160m which would be worse than something that you could fit into an attic. But it would not really be recommended for your introduction to ham radio. You have plenty of time to experiment with all the bands and learn as you go.

    Good Luck,
    Harry WB3BEL
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A loop following the perimeter of the attic makes maximum use of the available space, and nothing else does.

    To do anything else in an attic seems silly.

    WB2WIK/6
     
  9. G4ILO

    G4ILO Ham Member QRZ Page

    That's pretty much true, and I used one for several years. But a loop can present some really off-the-chart impedances in some bands, so it has to be matched at the feed point, or else you have got to bring open wire feeder into the shack somehow and use a wide range tuner.

    At these hard to match impedances, the losses in the tuner may well be somewhat more than the few per cent the manufacturer quotes. So a resonant dipole might end up working better on some bands even though it contains less wire. But an auto tuned loop will work to a point on most if not all bands, whereas with the fan dipole approach you can't really have a dipole for every band.

    In the end, the only way to find out what the best antenna is for your particular limited space situation is to try things.
     
  10. Pushraft

    Pushraft Banned

    Problem is, it is a royal pain in the a** moving around up there. The Yagi-Uda antenna I have up there now is relatively close to the access door so I can quickly get to it and keep the cable short. If I had to attach a wire to the perimeter of the entire attic that would be a big task. I wouldn't want to go up there and keep adjusting it either. Since the Yaesu FT-767GX is only rated for tuning 3:1 mismatches or better, I would likely run into some problems on some bands.

    Seems like this whole attic antenna thing and generic band antenna with tuner is a big compromise and I'll be lucky if I can go 100 miles with 100 watts even on the best band for my antenna. It still might be fun to try it and use the rig mostly as a scanner which I believe doesn't require a license.
     
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