Strong Fiberglass Mast Material

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by W7FS, Nov 26, 2018.

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  1. W7FS

    W7FS XML Subscriber QRZ Page

    Where does one locate thick wall fiberglass tubing to utilize as a mast for vertically polarized VHF/UHF yagi antennas? Would prefer something like 1.5" OD to fit into existing 2" OD/1.5" OD steel mast. It would be at least 5-8' in length to allow for the mounting of a vertical at the top, the cross polarized beam near the bottom. All the local businesses have no idea what I am talking about. If not fiberglass, what have you been successful with in your application? Living in the boonies has it's disadvantages too....
  2. ND6M

    ND6M Ham Member QRZ Page

  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    WA7PRC likes this.
  4. WB3BEL

    WB3BEL Ham Member QRZ Page

    I can't visualize how you intend to mount a vertical on the top of the mast and pass the coax to the radio down along the fiberglass mast without passing through the plane of the Yagis and creating the same problem as a metallic mast.
    If you plan to make a big loop of the coax behind the Yagi with or without a standoff, possibly that could work.
    If the Yagis are rear mounted, then the mast could be metal.
    A sketch of your plans might be useful.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, as noted by WB3BEL, if you want the mast to be transparent to RF for a vertical or X-polarized VHF yagi, you need to run the coax from the driven element(s) towards the rear end of the antenna boom and let it (or them) hang down "behind" the antenna for a wavelength or so, otherwise the coax running down the fibreglas mast creates the same problem a metal mast does: An undesired, untuned parasitic element in the radiation plane.
  6. K6CLS

    K6CLS Ham Member QRZ Page

    End-mount the yagi and run the coax behind the reflector element. The yagi coax needs to be routed that way too, so stand-offs can help both.
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    For longer yagis, the end-mounting may be impractical.

    But I've used long-boom yagis vertically polarized (had an M2 12 element 2m yagi mounted that way for point to point FM use) and it's easy to just run the coax down the boom to the back end instead of the center, let it hang down in a long loop (mine was about 12' long, hanging vertically before it looped back to the supporting mast just above the rotator) and use it. Works as well as end-mounting, but much easier on the mast, rotator, etc. since the beam is still mounted to its mast in the center (or point that is the center of gravity, anyway).

    The coax loop blows around in the wind, so it must be well supported at the reflector on the boom and also at the mast.
  8. K6CLS

    K6CLS Ham Member QRZ Page

    Yeah, good enough is good enough.

    End mounted super long yagis definitely have too much torque, and thus the ubolts will crush the fiberglass tube. Sometimes, one can hang counter weight off the rear. But much better to hang the balanced antenna in the CG midpoint. If the coax can be routed...
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Easier still to use two smaller antennas stacked side by side on a cross boom.

    Then, a metallic mast doesn't matter.
    K3GM likes this.
  10. K6CLS

    K6CLS Ham Member QRZ Page

    Yes! And, a tighter pattern, if that is desired

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