I've got a 20m EDZ that serves me quite well, so I thought I'd chime in
here.
The 4:1 balun isn't used on the EDZ, as the specific length of 450 ohm
ladder line specified by the calculator handles the impedance
transformation down to 50 ohms. You can use a 1:1 choke/balun to help with
common mode and convert from the end of the matching section of ladder line
to a coax feedline.
As far as the advantage of the antenna, it's two 5/8 wave elements fed in
the center, so it has about 3db gain over a standard center fed dipole on
the same frequency. That gain is broadside to the antenna, with nulls off
the end.
Hope that helps!
73
Matt
AK4MK
On Wed, Feb 5, 2020 at 2:35 PM <john@kk9a.com> wrote:
> The double zepp looks to me like a dipole fed with balanced line. What
> is the advantage to this antenna?
>
> John KK9A
>
>
>
>
> Ken Bauer WC6Y
>
> I thought this would be easy, but I’ve screwed it up. I’m hoping to
> get some insights from this group of antenna experts re the easiest
> way to proceed! Perhaps someone could model it for me?
>
> I used the calculator at West Mountain Radio:
> http://www.westmountainradio.com/antenna_calculator_zepp.php
>
> Looking for resonance at 10.120mhz. I ordered supplies from Davis RF:
> their balanced line / coax center insulator, 14awg solid copperweld
> and 16awg 19strand copperweld 450 ohm ladder line. I ordered a Balun
> Designs 4:1 current balun.
>
> The WMR calculator recommended a matching stub of ladderline 10’ 2.2”
> and each leg of the antenna as 61’ 3.1”.
>
> I thought I would add a half wavelength of ladderline to the stub
> thinking that this would present the same impedance present at the
> recommended stub length. Figuring a .91% velocity factor, I added
> 44.22’ to the stub for a total ladder line length of 54’ 5” between
> the center insulator and the balun. I temporarily set the antenna legs
> lengths at 61’ 5” and wound about 18” of overage back on the antenna
> wire leg towards the center insulator on each side.
>
> I hoisted this up to about 70’ , pretty much in the clear, other than
> some pine branches at each end. 10’ of RG-213 to my RigExpert AA-55
> Zoom dangling at about eye level.
>
> The SWR plot shows a dip at 10.9mhz w SWR of 3.7:1 and a dip at
> 13.02mhz w SWR of 2.7:1.
>
> Thanks in advance for any insights!
>
> 73,
> Ken WC6Y
>
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