Attic 5BTV?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7ZBO, Nov 20, 2018.

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  1. WA7ZBO

    WA7ZBO Ham Member QRZ Page

    Looking at limited access to my HOA restricted town house attic and owning a new Chushcraft 5BTV, I'm wondering if anyone has ever tried setting one up horizontally in an attic with multiple ground wires leading away in different directions.
    Thanks, Larry - Utah
  2. VA3VF

    VA3VF Ham Member QRZ Page

    Never heard of a Cushcraft 5BTV. If it's really a Hustler 5BTV, installing it horizontally is not a good idea.

    If you have space for radials in the attic, consider a dipole, even a multi-band trapped one will be better.

    That said, attic antennas require very careful installation, and I don't mean for radiation purposes, but for fire safety. BE CAREFUL!
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  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I wouldn't try that, a ground plane vertical isn't the best in terms of antenna balance to begin with and unless you can construct a very good set of multi-band radials in your attic you'll likely have a lot of common mode issues and RFI problems.

    You're basically talking about turning a multi-band trapped vertical into an asymmetrical trapped dipole where one element has tuned element lengths and traps and the other is wire segments presumably cut to length for each band, which ideally would mean cut to 1/4 wavelength for each supported band and set up in some kind of fan dipole arrangement. Do you have enough space in the attic for such an installation including the 'radial' lengths?

    If you have the horizontal span for a 5BTV plus any radials at all you likely have a pretty long attic. There are better solutions such as loaded or trapped dipoles, perhaps loaded fan dipoles, heck a pair of screwdriver antennas mounted back to back, a Cobweb or a host of other approaches.
    NH7RO likes this.
  4. K7MEM

    K7MEM Ham Member QRZ Page

    That might be interesting if you had two 5BTVs, one pointing in each direction. Then feed them from the center. You would effectively have a trap dipole. Although, with the rafters and electric wires, I have no idea what the feed impedance would look like or how the radiation would be. A antenna analyzer would probably help you the impedance issue. You would need a pretty long attic to contain them both.

    You could conserve some space, if you removed the 80 Meter resonator and only used 40 through 10 meters. You could possibly add 12 and 17 Meters, in fan dipole fashion, to the antennas without increasing the overall length. That may make up for losing 80 meters.
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  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    Hi Zebo (@WA7ZBO),

    I would test the waters by putting up a simple single-band horizontal dipole (say for 40meters, coax fed with a Common-Mode-Choke at the feedpoint) to see what happens. This will tell you how bad the RFI from your own house and others is. It will also give you an indication how to tune any other permanent multi-band antenna (effects of coupling to wiring and roof material).

    A multi-band fan dipole (or coupled resonator dipole [look it up in the ARRL Antenna book]) would be my choice. You have a means of supporting multi-band dipoles by stapling wire to the wooden trusses...

    Mike M.
    Last edited: Nov 20, 2018
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  6. NH7RO

    NH7RO Ham Member QRZ Page

    Looking at your QRZ page detail satellite view it appears that you have some trees on or adjacent to your property. Any chance of camouflaging your BTV (with different shades of green camo paint and easy-to-make leaf templates)? If done well no one would be the wiser and you'd be further from RFI sources in your home. Another trick is to mount it on a tilt-over and lay it over when not in use.

    You may have success with wires in your attic but I'm always skeptical about that; I suggest trying harder and think outside of the attic.

    If you do go with an attic installation I vote for a two-Scorpion dipole (expensive but worth it).

    For that matter, such a compact dipole could be mounted outside on a telescoping mast sunk into the ground and retracted when not in use---that's what Ron, NI7J does at his HOA home... (scroll down the page to see his pix)


  7. WB2WIK

    WB2WIK Premium Subscriber Platinum Subscriber QRZ Page

    I wouldn't put a 5BTV in the attic, either.

    You might support it using overhead strings or something, but it's not designed to be self-supporting when normally mounted from its base mounting bracket and they laid over horizontally. It will "sag" a lot (weight x gravity) and the sag might even deform the 10m and 15m traps, which are down near the base. I know some use tilt-over brackets for these verticals and may tilt them up and down frequently, but I never thought that was a good idea -- the antenna was never designed for that.

    A much lighter and easier to install system might be a simple wire trapped dipole (either flat or inverted-vee) that will at least be fairly "balanced" and not difficult to support.
  8. WA7ZBO

    WA7ZBO Ham Member QRZ Page

    Thanks guys....hi Mike. we moved from the land of trees to a 55+ HOA quad house. My counter poise wires wouldn't be noticed on the roof but that big aluminum tree would be. just one of the trade offs to get away from a house telling you what to do every day. (snow, leaves,grass, etc). I have a couple coaxial dipoles (20,40). I snake some 8X coax up a heating duct to the upstairs furnace room which has open venting to the roof. Plenty of time to experiment so I will be back with reports.
    Thanks again.
  9. WB2WIK

    WB2WIK Premium Subscriber Platinum Subscriber QRZ Page

    My house never tells me what to do.

    However, an HOA can.:)
  10. K3GM

    K3GM Ham Member QRZ Page

    A few years ago, I believe there was an article in QST of an outdoor horizontal BTV installation. I can't guess how long ago it was though.

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