ZS6BKW Antenna Review: 1000 QSOs later...

Discussion in 'Amateur Radio News' started by K0LWC, Dec 20, 2020.

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  1. VK2XTC

    VK2XTC XML Subscriber QRZ Page

    This ongoing saga continues.

    What I have discovered is that the ladder line section can be adjusted independent to the Horizontal section making it easier to tune.

    My ladder line section is 13.45m long , making it's Calculated 1/2 Wavelength = 150/13.45 = 11.15 Mhz
    Measuring Short / Open circuit for the VSWR dip = 4.430Mhz (open) , 9.040 Mhz (short) , 13.710 Mhz (open) 18.450 Mhz (short)
    Velocity Factor = 9.040/11.15 = 0.810
    150/9.040= 16.593 meters (Calculated Length)
    16.593 * 0.810 = 13.44M (Physical Length) - As measured

    So home made ladder line with PVC Coated Steel Wire Washing Line from the local hardware store has a Velocity Factor of 0.810. It's basically not very good for use as ladder line.

    The L2 section of a ZS6BKW is not , as some have stated, a 1/2 wavelength at 14Mhz (20M). It is actually 0.62 wavelengths.
    0.62 wavelengths at 14Mhz is 13.286meters and if the ladder line VF is 0.90 it would be a physical length of 11.957 meters.
    In my case it's VF is 0.810 so the physical length is 10.761 meters.

    Which means you need to tune the section L2 to 12.55Mhz for VF of 0.9 and 13.94Mhz for VF of 0.810. Not 14Mhz as some have stated.

    This of course aligns with what K7JOE has stated above as 39.5 feet converts to 12.039 meters for a 0.9VF ladder line.

    If it ever stops raining here (nearly a month now) I'll get out and test it with L1 connected at 2 x 14.250 meters long.



    Brian
     
    K7JOE likes this.
  2. K7JOE

    K7JOE Subscriber QRZ Page

    yes, this is why the ZS6BKW is a good antenna on 20 meters. It is what is known as an extended double zepp (or very close) and so it offers some gain, about 3 db, in the broadside in favored directions. As you note, it is not a half wave antenna. As you will find out, the simplicity of it is what makes it stay in the air - light weight and simple. The specific lengths make it work on multiple ham bands meaning it's an inexpensive solution for most hams who want to be active multiple bands - 40/20/17/12/10 and will load up fairly easily on 80.

    Let us know your performance results!
     
    Last edited: Apr 12, 2021

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