Monday, September 9, 2019

ZS6BKW Antenna

What else is there that's under 100 ft, at a minimum covers 40 and 20m with out the need for an ATU, and will work on 75m?

After considering a few ideas, I took a closer look at the ZS6BKW antenna which is an optimized variant of the well known G5RV. This antenna checks the boxes on these points:
  • Light weight - no traps, coax etc hanging.
  • Low SWR on 40 and 20m, can run ~1kW with the AL-80B.
  • Respectable gain on 20m if you have the luck or luxury of orientating the broadside to favor somewhere of interest.
  • Will work on 75m with the remote ATU I already have. It's essentially a 1/3 wave dipole, as such has reduced efficiency since the resistive component falls rapidly when a dipole is under 3/8 wave length.
  • Also covers 17, 12, part 10 and 6m with low SWR.

Spent a couple weeks reading everything I could find, and playing with models - one is included with MMANA-GAL, others can be found online.

Decided it was worth trying out. Initially I was going to order the parts from The Wireman and build it my self, but found a source of these pre-made cheaper and better built for $60 (normally $90) plus shipping from Amateur Radio Supplies => ZS6BKW G5RV 80, so went that route. 

Current setup:
  • Antenna apex at 50ft, ends in inverted V configuration.
  • K9YC inspired choke balun - 7 turns of RG-8X through two mix 31 clamp on ferrites.
  • Remote ATU between the choke and coax to the shack. 

How does it work?
  • Except for 15m, low SWR on six bands from 40 to 12m, parts of 10 and 6m.
  • Remote ATU dials it in on 75, 60, and 15m, brings the total to nine bands.
  • 30m is the odd one out, ATU fails to find a match in my case.
  • Performance on 75m wasn't great on transmit, but it's better than nothing. My OCFD is notably better on 75m being a full 1/2 wave on this band. This may be why the G5RV is popular, at 10ft longer than the ZS6BKW that might make enough difference on 75m for it to be "good enough".

Nine bands where only three need an ATU, with 93 feet of wire in the air is OK by me. 30m might be an issue for some, but you can't always win 'em all :-) 

Links to further information:

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