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[TowerTalk] Yagi Performance ( Was: Clarification Re: Painting a Roof To

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Subject: [TowerTalk] Yagi Performance ( Was: Clarification Re: Painting a Roof Tower and Antenna?
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Date: Tue, 5 Feb 2002 00:30:41 -0600
On Mon, 04 Feb 2002 Stuart Browne <> writes:
> no...but the performance of the C4XL is outstanding.
> Stu -- WH6H

So, you are basically testifying that a 2L Yagi with 4+ dBd gain 
is an outstanding performer,  which I don't dispute.
(I'm happy with my 'shortie' 2L40).

To get 2 more dB over a 2L Yagi, one needs to go to wide spaced 
3L Yagi's on 0.35 WL booms (24 ft on 20M), or a C31XR, or stack 
a pair of 2L Yagi's.  ($$)

To get yet 2 more dB, one needs to go to 5L or 6L Yagi's
on 0.75 WL Booms or go to a 4 high stack of 2L Yagi's,
for EACH band.  ($$$$)

It would seem that large *trapped* Tribanders potentially fall 
somewhere between a short boom full size 2L Yagi and good 3L 
Yagi's which is in fact about where the TH7 gains are from Roger Cox's
measurements (except on 10M where the standard dimensions
are optimized for 10M FM).  (10M  DX dimensions recommended)

In other words, one needs to go to a MUCH larger antenna system
to realize any significant improvement in gain over a full size 2L Yagi 
(or a 'multi-monobander set of 2L Yagi's), AND the full size 2L
Yagi's have better bandwidth than most trapped Yagi's, especially
the short boom single DE versions.  

The only advantage of larger trapped tribanders would seem
to be in greater F/B ratio which may or may not be useful,
depending on one's application (I prefer low F/B for contesting
from south central USA) and one's local noise environment.

No wonder the familiar Trapped Tribander designs are falling from
favor.  There still is one useful place for trapped elements and that
is in directors to break up undesired effects of longer elements.

The CC X7 is an example of an alternative modern design utilizing
a Log Cell DE, full size reflectors and a single trapped Director.

The 'open sleeve' trapped 15/20 DE with separate 10M close
coupled driven elements is another interesting use of traps
such as in the HyGain Explorer Tribander.  Separate full
size reflectors would enhance the performance of this antenna,
or at least a separate 10M reflector.  
(An A4 with an open sleeve DE...)

Actually, I expect one would find that a full size, 
horizontal DIPOLE, mounted on a tower, in the clear, 
with a ROTOR, is also a reasonably good performer,
benefiting from efficient ground reflection due to horizontal
polarization with NO sloping (inverted V) elements,
being in the clear, and rotatable.  The CC D3W trapped
dipole is very popular and effective on the (narrow) WARC bands.

I would say that MODELING has certainly improved our
understanding of antenna performance and provided us
with better choices in today's marketplace.

Tom  N4KG

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