[Towertalk] limitations of stacking

[WB9UWA Jim Shaffer]

Hi All,

It has been my observation in looking at short yagis in free space,
that a yagi with an already good front to side ratio my readily be stacked
with 3 db gain. If you start with a yagi with a poor front to side ratio,
such
as the elevation plane of a 2 element yagi, somewhat wider spacings can and
do produce up to 4.5db stacking gain.  This is because the influence of
the stacking pattern not only sharpens the main lobe, but also increases
front to side ratio at practical stacking distances. The big wheel and
simple
dipole is another antenna that can be stacked for 4.5db gain for the same
reason.

Having said all of that about free space stacking, when you are talking
about
real HF antennas over ground at practical heights there is generally less
stacking
gain because the elevation lobes for the individual yagis in the array do
not line
up perfectly for their respective gain peaks. This is why often single yagi
EME
stations show 5 db of ground gain on 2m and 4 yagi stations at low heights,
rarely show more then a few db of ground gain, and then over a more narrow
vertical angle.

Your mileage may vary.

73, Jim Shaffer, WB9UWA.


----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>
Sent: Friday, March 22, 2002 11:54 AM
Subject: Re: [Towertalk] limitations of stacking


> On Fri, 22 Mar 2002  Pete Smith <n4zr@contesting.com> writes:
> > Is there a theoretical reason why the gain resulting from stacking
> > two HF yagis over real ground is limited to 3 dB?  I have a model of
> two
> > C-3Es that shows 3.5 dB increase over a single C-3E in the top
> position.
> > I'm trying to figure out if this is a modeling anomaly of some sort...
> >
> > 73, Pete N4ZR
> >
>
> Are you looking at a fixed angle,
> or the peak response for each configuration?
>
> If you double the received energy, you gain 3 dB.
> It is hard to imagine how doubling the number
> of antennas could receive more than double
> the energy.  Typically stacks produce LESS
> than 3 dB peak gain over a single antenna.
>
> Tom  N4KG
>
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