Help building a 20 Meter(And maybe an 80M) extended double zepp
Although I already have a dipole cut for 160 meters, it's performance is not great, so I was looking into building first a 20M extended double zepp, then maybe cutting down the length of the 160M antenna to get a 80 M extended double zepp. What I am having an issue is is with the length of both the wire tops, and the feed-line (300 ohm).
Starting with the 20 meter EDZ, how long do I need to cut each side of the dipole (using 12awg solid copper wire, insulated.) And also, what is the proper length for the feed-line so I won't be attaching it to the 4:1 balun at a high impedance point where I'll be impossible to tune up on my rig. I am looking at a distance of 100ft of less for the 300 ohm feed-line to the 20M EDZ, and less than 200 or so feet going out to the big 160M dipole.
So, for the 20 M EDZ, what should the length of each of the sides of the dipole be? What is the proper length for the 300 ohm feed-line (the dipole will be less than 100ft from the house, so any multiples around 60-80 ft or so would be good.)
If I want to turn the 160M dipole into a 80M EDZ, again, what should each length of each side of the dipole be? How long should the feed-line be? I have about 200ft of 300 ohm ladder line ruining out to it now, but I can shorten or lengthen it a bit if needed.
Thanks in advance for the math problems!
I've had some interest in the same thing niggling at the back of my brain, so your post prompted a quick Google search which yielded this chart :
The same search produced this article, which goes into the discussion of feedline length :
I only glanced over both, but I'll be reading them in a little more depth later when I have more time to contemplate doing this, myself.
Last edited by N1KPW; 06-28-2012 at 10:00 AM.
Reason: link text didnt show up on post
Here is another site that has some good info.
Good day Dennis
A tid bit of information I hope you will find useful:
The EDZ gets its gain by squeezing the pattern down into narrower lobes. There will be a beamwidth of 35 to 40 degrees (bi-directional) where it will have more gain than a half wave dipole. In all other directions the half wave dipole will have more gain, and in the directions where the EDZ has a null, the gain of the half wave dipole will be a lot more than the EDZ (maybe 10 to 15 dB more). The EDZ is a good antenna if you have one direction that you want coverage and can aim the antenna. It is a poor general purpose antenna because the area coverage is low.
True, if it is a fixed wire EDZ---but not if it is rotatable (see W5DXP's version linked earlier)! Same gain as a two-element Yagi on some frequencies and still better than a dipole on others.
It is a poor general purpose antenna because the area coverage is low.
Only wish I had the space for a 44' rotatable EDZ!
An EDZ's length is ~1200/f so each side for 14.2 MHz would be ~83 feet. The feedline should be 0.18WL plus N*0.5WL, so for VF-0.9 it should be ~22' plus N*61.5' so something around 84' would be excellent.
Originally Posted by AB2UI
Using the above formulas for 3.8 MHz, each element of the dipole should be ~158' and the series section transformer should be ~42' long.
If I want to turn the 160M dipole into a 80M EDZ, again, what should each length of each side of the dipole be? How long should the feed-line be?
However, please note that an EDZ needs to be at least 1/2WL high to get the full EDZ effect and that's hard to do on 80m. Also please note that your 20m EDZ fed with ~84' of twinlead will be resonant somewhere around the middle of 80m. Save yourself the trouble of the 80m EDZ and just use the 20m EDZ for 80m operation. At a reasonable height, you probably cannot tell the difference in actual operation. Also, the 20m EDZ can be used on all HF bands with a tuner. IOW-IMO, your 80m EDZ would be a waste of time.
I have settled for a 33' rotatable dipole that works well 20m-10m. With a 64' length of twinlead, my IC-756PRO achieves a good match on 20m, 17m, and 12m. Take away 9' of twinlead and it tunes well on 15m and 10m.
Originally Posted by NH7RO
Last edited by W5DXP; 06-28-2012 at 03:37 PM.
73, Cecil, www.w5dxp.com
The maximum power transfer theorem works just as well for a non-resonant antenna as it does for a resonant antenna.
Since a wire version of an EDZ for 14.1 MHz has a total length of about 86.8 ft, (each side is 0.64 wavelength) it's a little difficult to rotate. It would be much easier to rotate a two element 20 meter Yagi. The Yagi also has a beamwidth of approximately twice that of the EDZ.
Originally Posted by NH7RO
The exact length to get 0.64 wavelengths varies a little with wire size, insulation, and height above ground, so you will see different formulas in different places.
Since an EDZ is a non-resonant antenna, the exact length isn't critical and you might want to vary that a little to facilitate the matching.
I found another side dealing with DEZ:
According to this each side should be 42' 3" for a total length of 84' 6".
I already have a large 160m dipole that tunes great on 20 meters. I was just thinking about sitting another dipole that would five me some gain a d hopefully be able for me to tune to 6m easier than the 160.). And yes I know I could just build a resonant antenna with coax cut for 6m but that seems rather boring. For this antenna I'll be using insulated 12 awg with 300 ohm ladder line in the middle going to a LDG 4:1 balun.
Oh. One more thing...... If anyone is handy with antenna modeling software I would LOVE to see a 3D model of this antenna. Figure that the dipole will be about 1/4 to 1/2 wavelength from The ground. Ground type is hard dirk and rock, like you would find in the woods.