You are correct. The horizontal loop gets its gain by not radiating very
much energy vertically. It's pattern looks kind of like a doughnut. A
horizontal loop will give you a few dB of gain but better than a yagi? They
have got to be kidding. Sounds like you should be teaching them about
antennas.
73
Jim W4KXY
----- Original Message -----
From: "John Geiger" <johngeig@yahoo.com>
To: <vhfcontesting@contesting.com>; <vhf@w6yx.stanford.edu>
Sent: Wednesday, April 16, 2003 8:46 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
>
>
>
> __________________________________________________
> Do you Yahoo!?
> The New Yahoo! Search - Faster. Easier. Bingo
> http://search.yahoo.com
> ------
> Submissions: vhf@w6yx.stanford.edu
> Subscription/removal requests: vhf-request@w6yx.stanford.edu
> Human list administrator: vhf-approval@w6yx.stanford.edu
> List rules and information: http://www-w6yx.stanford.edu/vhf/
|