[TowerTalk] Antenna Modeling Question Update

Tue, 24 Jul 2001 10:31:47 -0400

Hank,

You asked four questions:

1. EZNEC works fine.  You need to be an experienced Windows, PC and software
user to use it.  I have modeled all of my antennas/stacks/towers etc.  It is
able to show the interaction between the antennas on the same and on
different towers and their patterns very nicely.  I'm not sure what
navigation problem you had.

2.  EZNEC will provide answers for your questions about the performance of
the 10M stack, the 10 ele at the top, the 10 ele 10 and the 6 ele 20
interaction, etc.  No need to get opinions.  The model will tell you all you
need to know.

3.  Your last question, however, is not something EZNEC will answer.  That
is the question about the tower loading with all those antennas.  I'd
suggest you first look at a ROHN catalog, add up all of your windloads and
see which ROHN tower  of the height you need is in the ballpark, load-wise.
That is, which one will handle your loading just based on the ROHN
information in the catalog.  That will ballpark it.  You should have a PE
mechanical engineer do the complete analysis to assure yourself that it will
be safe.  You'll probably need that for any building permit as well.  Even
if you don't need a permit, the PE analysis will let you sleep better at
night.

4.  There are several ways to match stacks.  WX0B and Top Ten Devices makes
matching systems.  There's also the tried and true 1/4 wave coax matching
system (that I use!).   Putting a relay box switch on the tower adds another
point of failure.  Equal lengths of coax back to the shack with manual
switching of 1/4 wave matching coax eliminates that failure point.  Relay
switching is faster to perform than manual switching. So there are a number
of methods to solve the problem, each with their own advantages and
disadvantages.

GL es 73,

Bill, N3RR

-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of KD4OL@aol.com
Sent: Tuesday, July 24, 2001 9:44 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Antenna Modeling Question Update

I want to thank those of you who responded to my question.  Several
recommended W7EL's EZNEC V3.0 program.

I looked at his demonstration program but was unable to use it properly to
fit my needs.  I probably lack some software navigational ability.
Suggestions?

I intend to put up a 100 - 120 foot tower with either two or three 10 meter
yagis.    I have three Telrex 10 meter yagis in which I could use in a
stacked configuration vertically.  Two of them are 5 elements each on 23
foot
booms and one has 10 elements on a 45 foot boom.

I would like to get the best configuration for not only dx but for long
distance ground wave.  I thought that by mounting the longer boom yagi at
the
top, with the smaller ones lower, that would be the best overall.  However,
I
would like to be able to see what the experts think is best with this.

Also, I have a nice 6 element 20 meter Telrex that I would like to see if it
is possible to mount it at the top of the tower with the long boom 10 meter
yagi about 8 feet or so above it.  This would complicate matters, I suppose
but i am interested to see if it is possible for the tower to handle this.

I intend to use either a Rohn 45 or maybe 55 type tower, fully guyed.  I
would probably have to use heavier and stronger guys at the top section than
recommended by Rohn.   Don' t know how much to heavy-up.

I realize that I would need a matching system, perhaps from WX0B for the 10
meter system.  Of course the 20 meter antenna would have its own separate
coax.

Since I want to get it right the first time, and not do alot of
"maintenance"
or systems alternations later, I would appreciate the collective wisdom from
this fine group such as you all.  What do you suggest?

Hank
KD4OL

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List Sponsor: Are you thinking about installing a tower this summer? Call us
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