[Elecraft] End Fed Half Wave

[k3ndm at comcast.net]

Dave, 
There are two ways to approach a response, a discussion of the theory or a practical implementation. I usually worry more about the practical. So, here goes. 

A half wave antenna in a perfectly vertical position radiates energy at low angles with little to no energy radiated upward. a 1/2 antenna that is horizontal at a height of 1/4 wave radiates energy at high angle and very little to the horizon. Everything else is somewhere in between. The question you need to answer is do you want to work DX or local nets. Your antenna configuration should follow that answer. 

The physical construction of the antenna is more a matter of what you can install. For instance, do you have the trees in the correct location to hang the antenna horizontally? Do you have a support high enough to make your antenna vertical. Do you have only one possible support that is not high enough to go vertical requiring an inverted Vee configuration? Typically, the physical problems are far greater than the theoretical. 

My suggestion is that you install the antenna in a manner that will keep it from falling and as far from your station as possible. Figure out whether you are going to chase DX or nets, and then change the antenna configuration to maximize that. There is no single perfect antenna nor is there a perfect single configuration. Everything with antennas is a compromise, so stick one up and see what happens. 

73, 
Barry 
K3NDM 


----- Original Message -----

From: w7aqk at cox.net 
To: "elecraft" <elecraft at mailman.qth.net> 
Sent: Monday, September 22, 2014 5:49:41 PM 
Subject: [Elecraft] End Fed Half Wave 

Hi All, 

Here's a question for the antenna gurus among the group. It's about the 
best way to deploy an end fed half wave antenna. 

First of all, I assume most would say to put the entire antenna up in the 
air as high as possible, and in a horizontal plane. I understand the 
advantage of doing that. However, what about a situation where you only 
have one support? My first inclination would be to deploy the antenna like 
a sloper, with the far end at the top of the support, and the other end at, 
or near, the rig. I started wondering, though, about where the maximum 
radiation occurs. In a half wave antenna, the current max is more or less 
in the center of the antenna. So, would it be better to get the center of 
the antenna as high as possible (taking advantage of the one support you 
might have), and then maybe bending the other half back downwards, sort of 
in inverted vee fashion? That would be as opposed to just running the 
antenna up in a straight line to the top of the support, thus possibly only 
getting the center about half as high as the top of the support. 

Here's a more definitive description of what I am thinking about, and 
compares to the situation I have. I have a pole that goes up approx. 40 
feet. If I deploy the EFHW in sloper fashion, with one end near the ground 
close to the rig, the center of the antenna would only be at approx. 20 
feet. Also, On 40 meters (the band I would be using), the pole would need 
to be some 50+ feet from the rig. Alternatively, what if I move the center 
of the antenna up closer to the top of the pole, and have the rest of the 
antenna slope back down to another tie point? Wouldn't this be apt to work 
better, even though I have created something similar to an inverted vee? 

I know a couple of RVer's who do something similar. They have two poles in 
use, one of which is much taller. They deploy their antenna so that the mid 
point of the antenna is near the top of the tallest pole, then over to 
another shorter pole, and then back down that 2nd pole vertically--almost a 
somewhat slanted "U" shape. Their results seem to be decent, but I don't 
know if there is a better way to do it. Their method condenses the lateral 
space required to deploy the antenna, thus fitting within most RV sites. I 
don't know exactly what this does to the impedance at the feed point, but 
they use tuners to resolve any mismatch. The pole I have is somewhat taller 
than either of the ones they use. 

Anyway, I assume I could do the sloper approach without creating any serious 
issues, but I'm curious about what others think of the "vee" approach to get 
the antenna center higher. 

I appreciate any suggestions. 

Dave W7AQK 


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