[Antennas] Classic 20 meter Endfed Zepp

Fri Dec 9 10:06:10 EST 2016

Does anyone else tried a 20 meter End Fed Half Wave wire fed with a 1/4 
wavelength of TV twinlead (Classic 20 meter Endfed Zepp)? I've used one 
for my QRP operating quite a bit. See 
http://w0vlz.blogspot.com/2012/06/another-portable-antenna.html .
The EFHW designs I've seen have a one or more radials or counterpoises 
on the ground. This seems to me to be like using an off center fed 
antenna with half of the antenna on the ground. The classic endfed zepp 
does not require radials or counterpoises. The entire antenna is up in 
the air, not just the hot side. But an EFHW wire has a high impedance 
feed. That's why commercial versions have something like a 9:1 balun or 
transformer or matching network at the antenna feedpoint. This gets the 
load impedance down to the point that most turners can take care of the 
rest of the 50 ohm mismatch. Feeding the EFHW wire with a quarter wave 
of twin lead is another way to lower the feed point impedance to the 
point that typical antenna tuners can take care of the rest. Twin lead 
feed has the added advantage that no other radials or counterpoises are 
required. The entire antenna system is up in the air.
Here's my analysis/conclusions as I've compared my Classic 20 Meter Zepp 
to a 20 meter halfwave dipole at the same height:
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TV twin lead does have more loss then lots of other feed lines that may 
be used but it is light and we're talking about less than 15 feet of the 
stuff here. Estimates I've found on the web show .5 - 1 dB loss per 100' 
for dry, clean, matched TV twin lead. The loss for 15' then comes out 
around .1 dB. Since my intended use of this antenna is temporary 
QRP-in-th-Park sort of operating, keeping the twin lead clean and dry 
should not be a problem. If it's raining, I just QRT, packup and go home.
Loss due to mismatch at the antenna is the other issue. See K5DVW's Nov 
2006 QST article posted at 
http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf 
Assuming that the EFHW wire presents a 3000 ohm load to the 300 ohm 
feedline then the SWR is about 10:1. Extrapolating off the left edge of 
K5DVW's figure 1 chart leads me to conclude that this 10:1 feedline 
mismatch adds another .5 dB loss for about.6 dB total. Feedline loss for 
30' of RG-58 (about the most I'd want to carry any distance) feeding a 
matched dipole at 14MHz is .4-.5 dB.
The feedline loss difference between 15' of twin lead feeding an EFHW 
wire and 30' of coax feeding a dipole is negligible.
My classic 20 meter endfed zepp antenna with quarter wavelength feed 
does require a tuner. While in theory the feedline could be trimmed and 
stubbed to present a 50 ohm load to the transmitter (see 
http://www.mfjenterprises.com/antennatalk8.php ) it is sensitive to 
antenna configuration and adjacent objects. A tuner of some sort is 
required to take care of the variable mismatch, but, since it is close 
to 50 ohms, the tuner does not need to be "wide range".
Based on my observations for the 20 meter TV Twinlead Endfed Zepp -
- Some sort of tuner is required (built into many QRP rigs these days)
- Feedline loss is essentially same as coax
- Allows flexible deployment (Vee, L, vertical, sloper)
- No ground (or radial or conterpoise) requirement
- Light weight
- Entire antenna system is off the ground
- Usually requires only one support
- Optimized for one band but usually can be tuned as a random length end 
wire for other bands
Bottom line is the 20 meter classic endfed zepp should perform like a 
dipole at the same height and it is easier to put up. Keep in mind, 
though, that as this antenna is resized for the lower bands the feedline 
losses will go up unless better "twinlead" (such as window line or 
ladder line) is used.
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The above seems to fit my observations running with my KX3. I've even 
loaded it up on 40 and 30 and made contacts. I've not experienced any 
problem with RF in the "shack" either.
Other opinions/conclusions/analysis?
73,
Niel - W0VLZ