model for 100' vertical antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W5VQ, Jul 26, 2021.

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  1. KM1H

    KM1H Ham Member QRZ Page

    I had excellent DX results with a pair of bobtails at right angles in the late 60's. I then installed a 120' tower 200' away and put a Mosley 2 el center loaded Shorty 40 on top, only good for a rotary dummy load. Replaced with a 2 el linear loaded Hy Gain that filled in the holes of the bobtails. No modeling back then to understand what was going on.

    BTW the bobtail improved with radials at the coax feedpoint at least in Eastern NH which was all flat beach sand left from the glaciers 12 miles inland from the ocean. Simple and cheap to build.

    M0AGP likes this.
  2. M0AGP

    M0AGP Ham Member QRZ Page

    Good to know. I didn’t realize the bobtail was such a cool antenna - now I understand better the good reports people have had on it.

    I wonder if the classic bobtail could be fed the way we feed EFHWs nowadays (49:1 balun). Maybe that way if feeding it could make for a multiband bobtail?
  3. K8DO

    K8DO Ham Member QRZ Page

    Hang a delta loop off the tower near the top - corner up and standing off from the tower by a meter.
    Feed it at the top with a balun. Accept the fact you will have a 2:1 SWR and use the tuner at the rig.
    This gives you 7.5 dBi gain at 26 degrees above the horizon.
    This assumes you have the room to guy the bottom corners out far enough to spread the loop.
    M0AGP likes this.
  4. W9XMT

    W9XMT Ham Member QRZ Page

    Below is a concept that might be worth experimenting with for this installation/purpose. The radiation pattern on 40m is quite useful, for the conditions shown there.

    The gains shown do not include allowance for the ESR of a network needed to match the feedpoint Z to a 50 +j0 Ω source.

  5. W5VQ

    W5VQ Premium Subscriber QRZ Page

    I like to experiment, may give this a try.
    M0AGP likes this.
  6. W5VQ

    W5VQ Premium Subscriber QRZ Page

    This would be easy to do, I have a extra feed line in the conduit at the base of the tower.
  7. M0AGP

    M0AGP Ham Member QRZ Page

    I may be wrong here, and I have no experience feeding a delta loop, but I thought I read on another post in this forum that you ideally feed the delta loop partway down from the top on one side? Maybe this is so you get both of your current max points on the “sloper” legs? Maybe it would be a quarter wavelength down on one side, so that on the other side it’s a quarter wave down?

    Someone please jump in here and correct me!
  8. K8DO

    K8DO Ham Member QRZ Page

    Don't overthink it. Feed at the top with a simple balun and match the coax at the rig.. Easy peasy and on the air with a bodacious signal.

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