ZS6BKW / G5RV dipole with a cage element

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD7FQI, Nov 25, 2019.

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  1. KD7FQI

    KD7FQI Ham Member QRZ Page

    I have had the desire to try a new antenna at a cabin I can go to during the winter.

    I thought up the wild idea of a ZS6BKW or a G5RV cage :) I would like to use 2 or 4 parallel wires spaced 3” (7.6 centimetres) apart on the radiating element, each side joined together on the feed point and ends.

    I am open to suggestions on G5RV vs ZS6BKW lengths, small length adjustments.
    I have spacers for 3” made but I can make other sizes.
    I have 300 ohm and 450 ohm DX Engineering window line to use as the matching section.
    I have 500 feet (152 Metres) of wire to experiment with.
    I have trees spaced apart to get it level at 50 feet(15 metres) above ground.

    I have tried to model this adventure in the free version of EZNEC but I need some training on how to use the program.

    I have been very happy with single band cage dipoles fed with a good balun.
    I really like my folded inverted V dipoles fed with window line at my home station.

    Has anybody ever tried this before? Anybody have any other ideas about this?
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    The Zo impedance and Velocity Factor of the matching section is a critical element of achieving the lowest SWR on multiple bands simultaneously. The optimum Zo is about 420 Ohms, which is close to Wireman #552, which I have used for the ZS6BKWs I have built. Your 300 Ohm line is not useful.

    Here is a posting about the ZS6BKW I built for my summer home.

    Our local expert on this antenna is Cecil, who likely will chime in
     
  3. W5DXP

    W5DXP Ham Member QRZ Page

    The 20 segments in the free version of EZNEC are probably not enough to model a cage dipole. I haven't tried it so will model it later today after I take my sister to the doctor. One question: Is the purpose of the cage to achieve greater SWR bandwidth? My WAG is that a cage works best with resonant wires.

    Mike, I'm flattered but you are obviously one of the ZS6BKW/G5RV co-experts on this forum.
     
    K7JOE likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    That would be my gut feel as well...
     
  5. N2EY

    N2EY Premium Subscriber QRZ Page

    Why?

    What is the purpose?

    As @W5DXP points out, the free version only does 20 segments, which isn't nearly enough to model a cage dipole.

    What is the goal?
     
  6. KD7FQI

    KD7FQI Ham Member QRZ Page

    WA7ARK That is a very good post you referenced/posted. Thank you.

    I enjoy trying new antennas and like some experimentation.

    I am trying to achieve better SWR bandwidth or at least have less adjusting on my tuner when I go from one side of a band to the other.
    I have a small Johnson Viking Match Box, MFJ 974HB and a Nye Viking MB-V-A

    Right now I have a 190'( 58 Metre) Double Zepp that is slightly V shape in vertical and horizontal planes fed with about 150 feet of ladder line. I had to adjust the latter line length several times to get it to tune on any band.
    With this antenna using any of the tuners I have I need to change the inductance and or capacitance(s) all over the place, some of the time max out one of the values, get it to tune all the way across any band.
     
  7. K7TRF

    K7TRF Premium Subscriber QRZ Page

    FWIW, here's a quick and dirty model of a ZS6BKW fed with 50 feet of RG8X to the section of matching feed line.

    Here's how it looks when the antenna elements are built with #14 AWG wire:

    upload_2019-11-25_12-43-50.png

    Since it's not a low SWR match anywhere let's use the 10:1 SWR bandwidth as a reference, it's roughly 600 kHz

    Here's a version using 8" diameter wire instead of #14AWG. Yeah, that's not the same as say a 4 wire cage made out of typical antenna wire but it shows the impact of changing the effective diameter of the antenna elements:

    upload_2019-11-25_12-47-45.png

    The frequency of best match dropped substantially and the 10:1 SWR bandwidth actually decreased slightly. Sure specific results would be different with an actual cage construction but I expect you'd have to reoptimize this antenna in cage form, it would no longer really be a ZS6BKW and I'm not sure you'd achieve your goal of improved SWR bandwidth at the shack end.
     
    KA0HCP likes this.
  8. AJ5J

    AJ5J Ham Member QRZ Page

    Emphasis added to the part I wonder about---wouldn't it be better to try it as more of a fan with slightly shorter open-ended parallel elements? Might give you more bandwidth that way. Just a thought that jumped out at me...
     
  9. AI3V

    AI3V Ham Member QRZ Page

  10. KD7FQI

    KD7FQI Ham Member QRZ Page

    Thanks for the help. I thought is was going to perform better or the same at worse and be a waste of wire.
     

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