[Antennas] Classic 20 meter Endfed Zepp

Fri Dec 9 16:23:53 EST 2016

Since you are feeding it with a quarter wave line, the line Will not sppear as 300 Ohm but several kOhms at the antenna giving a much better match than you are estimating. Same principle as a J-pole.
Steven C. Blanchard (KD7KKC)
sdblanch1 at mindspring.com
 or
kd7kkc at arrl.net
-----Original Message-----
>From: Niel - W0VLZ <w0vlz at aggienetwork.com>
>Sent: Dec 9, 2016 8:06 AM
>To: antennas at mailman.qth.net
>Subject: [Antennas] Classic 20 meter Endfed Zepp
>>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:
>>***************************
>>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.
>>************************************
>>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
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