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

    Brian Austin’s recent article is here:

    For an inverted vee ZS6BKW at a modest height, he shows that the pattern on 20 meters is pretty horrible and the new variant much improved by using a flat top and folding the elements vertically. An inverted vee will work much better If you can deploy it higher and reduce the angle, as others have reported.

    I reported on yet another variant of the ZS6BKW in an earlier thread, in which I used an inverted vee configuration, but folded the ends vertical. Computer modeling is useful in visualizing the patterns.

    WB5YUZ and M0AGP like this.
  2. 2E0VSS

    2E0VSS Ham Member QRZ Page

    Just as a matter of interest,
    Can anyone give me the figures (Length and flat top) for the 300 ohm feed at a vF of 0.8 please
    Element size too..
    I know I know it’s has better VSWR figures with 400 ohm but I have a roll of 300 ohm here at present.
    Many thanks
  3. AF7ON

    AF7ON Ham Member QRZ Page

    Brian sent me this diagram, which he calls the “gherkin”. L1 is the antenna length, L2 the length of the matching section (velocity factor 1) and the hatched area where an acceptable match can be found.

    My antenna had a total length of 28 meters and an 11.4 meter matching section of 400 ohm window line. I measured the impedance of the window line as 410 ohms and its velocity factor as 0.86. This puts it just outside the gherkin, but matches on my main bands were good.

    300 ohm line is a little more challenging, with a smaller range of matching values.

    Hope this helps!

    Mike upload_2021-5-31_21-26-7.jpeg
  4. AF7ON

    AF7ON Ham Member QRZ Page

    An antenna length of 29 meters (95 feet) and a 300/0.8 matching section of 10.4 meters (34 feet) should be close.

  5. 2E0VSS

    2E0VSS Ham Member QRZ Page

    Thank you Mike..

  6. K7JOE

    K7JOE Subscriber QRZ Page

    Hi Mike, when i read the article, i THINK the height that Brian used in his analysis was 9.5 meters tall, or approx 31 feet tall. At that height, the ZS6BKW ladder line has to be dealt with as the length of feedline is 39 ft long. Anyway, It's clear there are some compromises that were made during this test.

    I can say that results of the ZS6 are satisfying with the antenna mounted at about twice that height (approx 60 ft, 18 meters high). It would be great to verify this anecdotal observation with plots and / or data modeling.

    So definitely something to be said about height.
    Last edited: Jun 1, 2021
  7. N3PM

    N3PM Ham Member QRZ Page

    Try this - eng.htm

    Mike N3PM
  8. 2E0VSS

    2E0VSS Ham Member QRZ Page

    I had seen that Mike but he gives three or four different measurements for the same feeder Z..
    Many thanks OM
  9. K1VW

    K1VW Premium Subscriber QRZ Page

    I’ve been intrigued by these, but haven’t built one yet because I don’t how to tune 2 variables efficiently. Mine would be a flat top.

    Does anyone know a way to do tuning in 2 steps? For instance if I make the top span, temporarily connect a coax to the center, and tune that like a simple dipole to some particular resonant frequency like 5.000 Mhz or 5.200 or whatever, and then I know the top is done correctly. Then I replace the coax with ladderline which I know is long and trim that achieve another particular resonant point? This seems much more efficient to me than experimenting with 2 varibles.

    I’ve got existing wire and ladder line, I didn’t buy Wireman #1234, so I don’t know VF or real impedance. I’m going to shoot a line over a couple of tall trees i have, I don’t know how high it is, I can guess 60’ but I really know. It seems to me, the above 2 step approach could allow us to use what we have, in our real world location.

    Or maybe it doesn’t work that way, the length of the flat top is a resultant of the parallel feedline we inflict upon it.

    Thank you,
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    When building G5RVs or ZS6BKWs, most folk use the window line originally made by CCS, which was taken over by JSC, and more recently by a third party and still sold under the original CCS numbers by

    Actual measurements, here:

    Dan has these numbers inside TLDetails and AutoEz.

    Folks building G5RVs or ZS6BKWs should pay attention to the measured values of Z0 and Vf.

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