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[aprssig] Helix Groundplane?

Steve Noskowicz noskosteve at yahoo.com
Wed Dec 12 23:55:12 UTC 2007


  Uh... Life should be so simple.
     The  "gut feel" bone in my long-ago educated head makes me say hang on
just a bit.  The ground plane is behind the antenna in this case... while the
reflection of the incoming signal is in the front.  The aforementioned bone
first wants to argue that, in this case, two wrongs (may) make a right....
  "180 degrees " from the reflection combined with arrival from the back of the
antenna sounds like it could make it a wash and give what sounds like the
obvious 3 dB improvement.
  Then again, right-hand is right-hand from either direction and the reflection
of a right hand is left-hand...hmmm...
   Then...then  Approaching this from another school of thought, if the plane
really is a "ground plane", it MUST have a reflection.  An image, as we learned
in fields class, using the "method of images" (a mirror is a perfect analogy),
WILL have an effect on the antenna pattern and feed point Z.   Stop me, stop
me, my brain hurts.

Any helix experts out there?

73, Steve,


--- Robert Bruninga <bruninga at usna.edu> wrote:

> > Helix antennas being circulary polorized have 
> > rejection to the opposite rotation generaly 
> > caused by reflections provided that both...
> 
> Wow, interesting.  I just realized then, that the "reflector
> screen" at the back of a Helix is not adding any gain then.
> Because it is true, that any reflected energy will be the
> opposite circularity! Thus it cannot add in phase to the direct
> wave.
> 
> I guess all the ground plane is doing is providing a
> counterpoise for the feed system.  Oh, and possibly a degree of
> attenuation to ground noise...  Both well worth the metal, I
> guess.  Comments?
> 
> Bob, WB4APR
> 
> 
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-- 
73, Steve, K9DCI


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