My initial thought is that the proximity of the vertical to your tower will
result in quite a bit of mutual coupling between the two. The coupling
effects would be minimized if the resonant frequency of your 40M
tower-antenna is far removed from 160M.
This isn't necessarily bad, but it will affect the lengths of your wires as
far as resonance on 160M is concerned. Whether or not you can achieve a
35-ohm feed impedance would be a good question.
>From a pure modeling standpoint, there isn't much difference between a
flat-top T and a T with a downward tilt to the arms. This is particularly
true with a tall Tee (like yours would be) with relatively short arms.
When all is said and done a simple L would do just about as well, and it
would also have the same mutual coupling questions.
------------------ Wes Attaway (N5WA) ------------------
1138 Waters Edge Circle - Shreveport, LA 71106
318-797-4972 (office) - 318-393-3289 (cell)
Computer Consulting and Forensics
-------------- EnCase Certified Examiner ---------------
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Robert Pack
Sent: Monday, November 23, 2009 11:01 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Variation of Vertical T
I have a bit of a dilemma for the short term. While the construction is
going on to erect a true elevated 160m vertical (36 foot high base,
insulator then 120 feet above that) I need an alternative vertical for 160.
My preferred choice at the moment is a top loaded T but current
circumstances just are not going to allow me to string up such an antenna
between towers. I had to remove the one I had up......or better
yet........mother nature removed it for me and I cannot put it back up right
now.
I do not want an inverted L although it is probably the easiest thing to
do....but I do want a vertical. I also do not want to shunt feed a tower
and put down miles of radial wire.
With a top loaded T antenna in mind.........I put the vertical wire on
supports up my 40m tower with the feedpoint 10 feet above the ground to a
point at 105 feet up the 40m tower (95 feet of vertical wire) and instead of
the top loading being in a T configuration I just slope those two wires at
45 degree angles downward.
Does it matter if the top loading wires are really horizontal or can they be
sloped as described above?
I am assuming the feedpoint will be about 35 ohms so a pair of 75 ohm lines
should accommodate that ok.
Anyone have any valuable input on this issue?
If I can make it work it will be a nice backup antenna for the future.
Bob NX5M
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