Hang 2m/70cm antenna in Attic?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KF5LJW, Mar 24, 2019.

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  1. KF5LJW

    KF5LJW Ham Member QRZ Page

    Any reason why not?

    Example say a Comet GP3 Dual Band 2m/70cm hanging from para cord.
  2. K5TCJ

    K5TCJ Premium Subscriber QRZ Page

    The only reason i can see is if there's a Radiant Barrier under the roof.

    Take a look at this, as an example of mounting a VHF/UHF antenna to a drain vent stack on your roof.
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Should work, but definitely not optimum.

    Attenuation of roof material, reduced height, possible coupling to the house wiring, are just a few of the things that can have a negative effect.

    Your experience with cellular telephone sites should answer your questions.

    Glen, K9STH
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    I don't see any reason why it shouldn't work. Electrically para-cord or Dacron rope used to suspend the antenna hitched to the element hanging from a roof rafter should be invisible to the antenna. Don't think it makes any difference whether it is held up on a mast as designed, or hanging from the element. Its a Ground Plane Vertical in correct orientation. Granted in an attic is not optimal, but given either way will be in the attic should not IMO make make any difference in mounting methods. Not my attic anyway. :)

    Yeah it should work. Never hurts to get a 2nd opinion. The attic is huge and pretty much open. Gotta be 15 feet clearance or more above. That will put the base above HVAC plenum and all house wiring. That is what he gets for living in a HOA. 144 attenuation should not be significant, 444 some but no show stopper. Better than a HT. :)
  5. KN4CQB

    KN4CQB XML Subscriber QRZ Page

    I had an end fed Ed Fong antenna at my last QTH and it worked great. New house not so much
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Location and building construction materials can make a big difference.

    A house on a hilltop of all wood construction and siding, without foil backed insulation, and asphalt shingles above is a good application.

    A house with stucco siding, aluminum siding or any kind of cement or brick siding, or one with foil backed insulation, or a metal roof or cement tile roof can be a problem. A house in a valley might also be a problem!

    My simple "test" when reviewing possible houses for purchase is to bring a cheap FM broadcast radio up into the attic, first tuned to a weak, distant station that isn't very strong when standing outside the house. If it's "weaker" in the attic than it was outside, that's not a good sign.:p
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    Thanks for sharing. Never thought of using a vent pipe as a mast support. Telescoping like that should work as long as no strong winds, or try to put too much weight and mass up high. Although if he had the option of an Outdoor Rooftop Install, we would not be having this discussion.

    I don't think Radiant Barriers are an issue. I don't recall seeing one, just plywood decking and asphalt shingles. That should not attenuate signal significantly. We can get it above HVAC vents and wiring by a couple of feet. Not ideal, but good enough to work local repeaters. We hit all repeaters with an HT up there with good signal reports. Our Rx was fully saturated. So conditions should be better with a base antenna vs Rubber Duckie of an HT.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Go for it.

    It may be the only limitation of an attic VHF-UHF vertical is its height above ground. Obviously, outside and above the roof it could be higher.

    Geometry is a powerful thing.:)

    But if this is for repeater work within 50 miles or something, it probably doesn't matter.
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    To my knowledge, just repeater stuff. He lives in an area of Tulsa called Sheridan Hills on the south side of Tulsa and he lives on the northside of the hill. From his window you can see all of Tulsa in the valley below and points north a good 40 miles. We can hit just about all repeaters with an HT and Rubber Duckie.

    My question was oriented toward electrical performance (VSWR, Impedance), and whether or not hanging it vs mast mount make any difference? From my experience and answers here indicate no issues with that respect. Other than being confined, no other known issues. I expect higher noise, some pattern irregularities, and some attenuation.

    One improvement guaranteed hanging it not many can do for long if at all. It will have perfect Vertical orientation. It will be a great Plumb Bob. No wind or movement. :);):p
    Last edited: Mar 25, 2019
  10. AA5CT

    AA5CT Ham Member QRZ Page

    @KF5LJW actual cellular coverage planning or local 'booster' installs (as sometimes were used in RSA sales offices) should inform one that just getting above the walls (bricked, stucco w/screening inside, etc) buys one many dBs of signal gain ...

    And you're not just 'fighting' your own house's brickwork or stucco either, but your neighbor's as well (in a subdivision) ... The only problem with an antenna meant for outside is - how hot will the attic ultimately get and will the antenna innards do anything funny in those conditions?

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