[TowerTalk] Shadowing of small antennas by larger ones?

[Guy Olinger, K2AV]

Not going in circles for me.

Proof?  It's not like this is an unvalidated/unmodeled antenna from a
fly-by-night company, though we unfortunately do have some manufacturers
of that ilk. For general purposes do I need other than the two antennas
are interlaced on the same boom and sold as a single antenna, and that
F12 recommends 8 feet or more for vertical separation if sold
separately? They use a paid contractor for their NEC4 modeling, and have
done the work up tower for validation. If I was looking for something to
be worried about, I would find something else with some likelihood.

BTW, to one other poster, the EF240 and 240N are rather DIFFERENT
antennas.  Spacing requirements are different as well.

-----------------

Guy Olinger, K2AV
Apex, NC, USA

----- Original Message -----
From: Tom Rauch <w8ji@contesting.com>
To: <n4kg@juno.com>; <towertalk@contesting.com>; Guy Olinger, K2AV
<k2av@contesting.com>
Sent: Wednesday, January 31, 2001 5:57 PM
Subject: Re: Re: [TowerTalk] Shadowing of small antennas by larger ones?


> Hi Fellows,
>
> > Read the description carefully. On the C39, the 40 DE is BETWEEN the
> > 15 DE and the 15 reflector, NOT behind the 15 reflector.
> >
> > They HAVE had to deal with removing the 21 mhz resonance from the 40
> > "N" elements. The diagram is at home, but the distance from the 40
DE
> > to the 15 DE on the same boom is a LOT less than the vertical mast
> > separation the original poster proposed between the separate
antennas.
> >
>
> This seems to be going in circles.
>
> Has anyone modeled this or measured it?
>
> It is important to stress that even without resonance a large
> structure  in the nearfield can affect performance greatly. We all
> deal with that every day, but when it comes to antennas we seem
> to toss it all out and assume if it isn't resonant it can't affect the
> system.
>
> I know for sure it will affect the smaller antenna, the question is
> only if it is enough to worry about.  Do any of you know the answer
> with some convincing evidence?
> 73, Tom W8JI
> w8ji@contesting.com
>


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