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Building a ZS6BKW

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N6UM, May 31, 2021.

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  1. AF7ON

    AF7ON Ham Member QRZ Page

    Yes, most of Brian’s tests used antenna heights in the 30-foot range.

    I haven’t yet run a simulation for a higher inverted vee, but expect that the pattern on 20 meters will be significantly improved. The poor pattern results from interaction with the mirrored elements in the earth and these should improve with height. Poor soil may also help.

    But these are all theory - there is nothing better than on-air testing!

    K7JOE likes this.
  2. M0AGP

    M0AGP Ham Member QRZ Page

    I agree with what Joe said - it would be interesting to see the 120 degree apex angle inv-vee-ZS6BKW radiation pattern on the higher bands as a function of height. Maybe just 40 feet, 70 feet and 100 feet?

    I have a model for EZNEC, but being a cheapskate I didn’t pay up for the full model - so my results would be “suspect”...
    K7JOE likes this.
  3. K7JOE

    K7JOE Subscriber QRZ Page

    It would be great to see the modeling as follow:
    at 30, 45 , 60, 75, 90 ft (reasonable placement heights for most situations)
    A. flat top configuration
    B. Inv Vee configuration at same with angle 120 degrees
    C. Inv Vee configuration at same with angle 90 degrees

    perhaps someone can model the pattern for each of the main bands (40-20-17-12-10)

    By the way, I do acknowledge and agree that a "low" ZS6BKW in inverted Vee config (30- ft height) as tested by Brian Austin, does not work as well as a dipole inv Vee on 20M due to high angle of radiation lobe of the ZS6BKW. But at double that height, i see no degradation, rather, I do observe some end-fire gain compared to inv V at same height. anecdotal data through actual on air tests.
    Last edited: Jun 1, 2021
    M0AGP likes this.
  4. K7JOE

    K7JOE Subscriber QRZ Page

    Think of this as an antenna system comprised of a length of wire and a length of ladder line. The ladder line, while a feedline, acts as a tuning stub and so what you are doing by changing the length of the ladder line is to adjust the antenna system and tuning it to Z50 on multiple bands. I would start with what is easiest -- change the length of the ladder line since it is closer to ground - once the antenna is mounted in place and far easier to snip and adjust a small piece of ladder line than lowering the antenna, adjusting element length and re-raising antenna multiple times. Certainly there is interaction between A and B, but since my goal is to tune the antenna system, I would go for the easier adjustment first, always...

    I've cobbled these together totally unscientifically and they work fine. 46 ft elements, 39 ft ladder feed-line and go from there. One sweep with an analyzer will reveal if too long or not.
  5. M0AGP

    M0AGP Ham Member QRZ Page

    OK - I pulled up the model for my (never-built) doublet. It is not quite a ZS6BKW - I intentionally slightly "detuned" it so that a remote tuner I had my eye on would be able to dial the thing in on all the desired bands. I first show the radiation patterns for my version and then I simply increased the height equally for all the wire endpoints so that the thing has a peak at 65 feet. So Joe, the 2nd antenna (next posting) won't be the same antenna you have but it will be my detuned version with the peak at 65 feet and about 120 degree apex angle.
    upload_2021-6-3_17-46-13.png upload_2021-6-3_17-46-37.png



    Attached Files:

    Last edited: Jun 3, 2021
  6. M0AGP

    M0AGP Ham Member QRZ Page

    And now the case with everything moved up an equal amount so that the peak is at 65 feet instead of the odd value of 36.7 feet, and the apex angle stays the same:

    Well, it looks better on 15 and 12 meters...

    Actually one important thing to point out is that these are very complex 3D shapes and I am only showing one cut through the shape. So it may be that a different cut would have better low angle lobes?

    And again this is not strictly speaking a ZS6BKW - it is a detuned version that would allow an easy match on all the bands of interest using the Stockcorner tuner I had in mind.

    So I can't draw any hard conclusions from this but thought to show what I could show!

    And of course in theory, theory and practice are the same, but in practice they are not...
    K7JOE likes this.
  7. AF7ON

    AF7ON Ham Member QRZ Page

    I ran three ZS6BKW simulations - a flat-top at 40 feet, a 90-degree inverted vee at 40 feet and the same inverted vee at 60 feet. I just took a quick look at the patterns on 20 meters over poor soil at a low 10 degree angle. For the 40-foot high antennas, the low inverted vee is about 7 dB down on the flat top and the high inverted vee gains 6dB over the lower inverted vee, coming close to the lower flat-top. The higher inverted vee develops some broadside gain with two low lobes not seen when it is closer to earth.

    I'll run some more simulations and report back in a day or two, but initial results suggest that the inverted vee configuration of the ZS6BKW can work fine if you get it up high enough. A flat-top seems best overall, but if you are limited in height to less than 40 feet the new configuration with vertical ends looks better on 20 meters.

    K7JOE and M0AGP like this.
  8. 2E0VSS

    2E0VSS Ham Member QRZ Page

    It may or may not be of interest to you folks to seek out the paper from ZS1AN, Andrew (A better tuner balun) Roos (Call changed now) He worked on various Variations of The ZS and G5 and presented his work of related Matched losses etc etc on a couple of variants to the Radio club of Cape town some 15 years ago, hes a sharp cookie and hes not .....a "Hammy Sammy" Hes Old school but informed..
    K7JOE and M0AGP like this.
  9. M0AGP

    M0AGP Ham Member QRZ Page

    This sounds reasonable, that height can help with the radiation pattern. I must admit that after seeing how complex even the 20m inv vee ZS6BKW pattern was, it was hard to get an intuitive picture as to what is going on with the various lobes. Once you get to an antenna that is materially longer than a half wave dipole, it gets harder (for me at least) to imagine what the various lobes will do as you change the apex angle, and also the height.

    Maybe a free-space version is the best place to start, using a flat ZS6BKW, then start drooping the wires a bit at a time and watch what the lobes do.

    Once that behavior is intuitively understood, then start bringing the height down to see what that does...
  10. K7JOE

    K7JOE Subscriber QRZ Page

    Good analysis. It proves, at least in part, what I see on 20M+ at the 60+ft height . Now expanding from a 90 degree angle to 110 or 120 degrees should increase the low angle lobes on 20M and this is very close to the pattern of the extended double zepp antenna.

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