John,
Think about this analogy. Place a round balloon on a flat surface, put
another flat surface on top of the balloon and apply pressure. The balloon
will change shape spreading out horizontally but does not get larger in
volume. This is similar to what happens when antennas are stacked
horizontally.
David
----- Original Message -----
From: "John Geiger" <johngeig@yahoo.com>
To: <vhfcontesting@contesting.com>; <vhf@w6yx.stanford.edu>
Sent: Wednesday, April 16, 2003 11:46 PM
Subject: Gain from an omnidirectional antenna
> I have an antenna question for the reflector. On the
> local repeater here, the general consensus is "Get a
> horizontal loop for VHF, they will outperform yagis".
> (I know better, but hey, I just report what I hear).
> So here is my question-I have heard gain figures
> attributed to loops, or to stacked loops, but I don't
> understand how. If an antenna is truely
> omnidirectional, where does the gain come from?
>
> As I understand it, a beam gets its gain from focusing
> its RF in the forward direction. It takes the
> radiation that would go to the front and sides, and
> compresses it into the forward direction instead-or
> something like that. The gain comes because you lose
> radiation in other directions. But if an antenna is
> onmidirectional, it is not compressing the signal into
> one direction more than the others. So how does it
> get gain? The only idea that I can come up with is
> that it must cut down on the vertical lobes, taking
> the energy from several of the vertical lobes and
> focusing it into one or two vertical lobes. It can't
> do it in the horizontal plane, or then it wouldn't be
> omnidirectional.
>
> So am I even on the right track with this question or
> thinking? As you can tell, the local club really
> needs a good course in antenna fundamentals!
>
> 73s John NE0P
>
>
>
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