ZS6BKW Coax Question

Discussion in 'General Technical Questions and Answers' started by W8AMD, Jul 17, 2019.

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  1. W8AMD

    W8AMD Ham Member QRZ Page

    Hey everybody.

    Had a question about setting up a ZS6BKW G5RV antenna. I read somewhere that it required 75’ of coax from the radio to the ladder line for tuning reasons. But after I read that I couldn’t find it again anywhere I looked. So anyone that has used one did it work with less coax? Or are you using it with 75’?

    I just feel like 75’ would be pretty lossy even at HF. Plus not to mention I don’t THINK I need that much Coax to put it up. Thanks
  2. W1VT

    W1VT Ham Member QRZ Page


    The article on the ZS6BKW written by Brian Austin makes no mention of that length. Brian invented the antenna and this article provides commentary on the design. If you subscribed to SPRAT back then you were among the first to know.
  3. N6RGR

    N6RGR Premium Subscriber QRZ Page

    I am using less (maybe 45-feet of coax). I am using a 1:1 isolation balun at the end of the ladder line. It works fine. Make sure you keep the ladder line fully elevated in the air at right angles to the antenna. Mine is in an inverted V configuration with the top at about 46-feet allowing the ladder line to be in the air.

    Roger N6RGR
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    The ZS6BKW does not need a specific length of coax. It's likely some ham posted that they had good luck with 75', but the design of the antenna doesn't require that exact length.

    That said, if you run decent coax you shouldn't have a lot of loss at HF with 75' of coax at least on the bands where the ZS6BKW presents a half decent match to 50 ohms. You can get an estimate of coax loss for different coax types and variations of: run length, operating frequency and SWR here: https://www.qsl.net/co8tw/Coax_Calculator.htm
    WA7ARK likes this.
  5. W8AMD

    W8AMD Ham Member QRZ Page

    Ugh it’s gonna be pretty hard for me to get it up that high...
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    It doesn't necessarily have to be that high but ideally the section of matching balanced feed line will run at right angles to the antenna for its entire length. Hanging straight down is great if you have enough height but as long as it runs perpendicular to the antenna, even straight horizontal or sloping it should still work fine.

    What you don't want is to have that section of matching feedline run along parallel to either of the antenna elements nor do you want it coiled up or running up against a house or tree, lying on the ground or worse, running up against metallic objects like rain gutters. You can use spacers to keep the balanced feed line away from objects but ideally that section of matching feedline would be in a fairly straight run that's perpendicular to the antenna elements. If that's not possible at your QTH then you might consider a different antenna design.

    The coax portion of the feed line run doesn't need any special consideration but the twin lead or ladder line matching section does.
    Last edited: Jul 17, 2019
    N6RGR likes this.
  7. N6RGR

    N6RGR Premium Subscriber QRZ Page

    You also might want to read Cecil's (W5DXP) insights on using a ZS6BKW. He has modified it to be more friendly on certain bands (15m, 30m, 80m). It does pretty well on 40, 20, 17, and 12 meters in my experience.

    Roger N6RGR
    WB5YUZ likes this.
  8. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Since impedance transformation is supposed to be handled by the balanced line length, it is possible someone chose 75 feet to avoid accidentally making the coax run into a 1/4 wave transformer on 40, 20, 17, or 12m, the bands the unmodified ZS6BKW works best on.
    K7TRF likes this.
  9. W5DXP

    W5DXP Ham Member QRZ Page

    AG5CK and WB5YUZ like this.
  10. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Or unwanted transformations!

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