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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