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[TowerTalk] The dumb kid returns.

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Subject: [TowerTalk] The dumb kid returns.
From: (L. B. Cebik)
Date: Sun, 22 Feb 1998 07:01:25 -0500 (EST)

At a certain point, you will have to balance all the advice you receive
and add in some factors that are unique to your situation.  Try the
following for an example.
1.  How much money are you willing to spend and how do you wish to place
it?  Some will go to the tower and installation.  Some will go to the
rotator, which must be sized to comfortably handle whatever antennas you
turn with it.  Some will go for antennas.  Some will go for cables.  and
some will go for miscellanea (local permissions/inspections, ground
systems, etc.)
2.  How much horizontal and vertical space do you have or are you willing
to use for the antennas.  Quads are 3-dimensional and do not allow
"snugging" up a wire antenna under them at as high a level as a
2-dimensional Yagi, etc.
3.  What are the practical ("I have to live with them") neighbor

Hence, good advice and experience on sucess with antennas can only go so
far.  The rules of thumb you likely have already heard tend to play true
when you do not have to make site variations to accommodate the move from
one idea to another.  For example, the C-3 tends to equal on each band
what a monoband antenna of the same number of elements and boom length for
each band would achieve.  This cannot be said of the simplest
3-element-3-traps-per-element designs, since they are a compromise in all
respects.  However, some of the Force 12 bigger designs and some of the
other multi-band designs with no traps in the driven elements will provide
more performance, since they have more boom length and usually more
elements per band.  There are good multi-band designs out there.

A good 2-element quad for 5 bands, at least with separately-fed driven
elements via a proper switching system, can come very close to max
possible quad performance for 2-elements on all 5 bands.  This figure is
greater than a good 2-element Yagi, but under a long-boom 3-element Yagi,
and may approach the gain and F-B of some short boom 3-element Yagis.
However, it is a more complex 3-D structure that many folks find harder to
maintain.  Quad shortcuts with respect ot feed or structure may not yield
the full performance noted here.

At lesser gain, but greater simplicity of structure are antennas like the
LPDA, which will in the best commercial versions do better than 2-element
Yagis in the shorter, low-element-number designs and approach 3-element
Yagis in the longest, highest-element-number designs with a relatively
smooth SWR over the entire frequency range.  Most commercial designs are
2-D.  However, because of their greater bandwidth, LPDAs may give less 
gain and F-B than some multi-band Yagis of equal weight and space
which might do more per band.

Mechanically, integrating a high 40-meter element or antenna into a single
tower array requires extensive "engineering," with considerations of
interaction and moments of force.  As a first installation, it may require
excellent but perhaps costly professional assistance to make it work and
stay up.

Since you have pretty well decided on the tower size, you might consult
the extensive archives of Towertalk to fully appreciate all the the
details that will go into a very good tower installation of that size.  As
you digest that material, you will get a good sense of how much antenna
weight you can support.  This information can then be integrated with your
antenna space, budget, and operating goals to reduce the range of
possibilities to a smaller number.  Acquire all the antenna literature you
can obtain for the possibilities--these catalogs and brochures will answer
a lot of questions about size and weight--and even some on interaction and
performance.  Do not go just by small advertisements or casual comments.
All comments, even the general ones above, have to be integrated into a
total pattern of detailed information about each possible antenna that
might meet your space/weight/budget/operating goals and constraints.

With this background info fully digested, you will even know how to take
advantage of that occasional great deal that comes along--say one that
meets your space and weight limits, gives you x% of your operating
desires, but saves you y% of your budget.  I like to make charts, after
fully determining what to label each category of concern and how to weight
it in my decision making.  Filling in the blanks from detailed literature
(with some spec numbers checked out with experts to be sure they are
reasonable claims) often makes the decision for me.  I even compile the
comments I receive, especially the one that tell me exactly the perfect
system (the one they use) with notes on how similar their situation is to
mine.  The trick is to move from receiving advice to analyzing all the
details that such advice involves--the unsaid as well as the said.

Remember, if the antenna falls, it is your liability.  If it fails to give
the performance you think it should from the comments received, there are
a thousand excuses we advisors can give.  Hence, my bottom line is not to
spend the dollars until you are able to know what you will get for them.
Right now, my best suggestion is that you send off for every one's
detailed catalog and spec sheets so that you can begin making your own



L. B. Cebik, W4RNL         /\  /\     *   /  /    /    (Off)(423) 974-7215
1434 High Mesa Drive      /  \/  \/\     ----/\---     (Hm) (423) 938-6335
Knoxville, Tennessee     /\   \   \ \   /  / || /      (FAX)(423) 974-3509
37938-4443     USA      /  \   \   \ \       ||    

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