[TowerTalk] Insights on 30m EDZ - nowhere near what I thought

[john at kk9a.com]

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