Herb,
I have been thinking about building the same type of antenna that Charlie
has in mind. I have two questions:
1) You say to connect the top wires together end to end. I think that mean
at the ends of each top hat wire? From a top view, the top loading wires are
attached at the top of the vertical radiator and strung out as you
recommend, then connect their ends to each other with more wire to make a
large triangular top hat, correct?
2) If I build such a 160m loaded antenna and want it load it on 80m, could I
drop the three top loading wires and attach them to the vertical radiator
wherever they hang down to, then build a separate 80m matching unit? To
switch back to 160m, I would detach the top loading wires and string them
out to their original tie points and change back to my 160m matching system.
I see no reason why this would not work. Any comments?
I wish to thank you for all your past inputs to the Topband. Many are filed
away for future reference.
Tnx,
Ray,
N6VR/7
Prescott, AZ
-----Original Message-----
From: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
On Behalf Of Herb Schoenbohm
Sent: Tuesday, May 04, 2010 5:51 AM
To: Charlie & Vivian Vaughan
Cc: topband@contesting.com
Subject: Re: Topband: Top Loaded Vertical
Charlie K4UWH Wrote:
> I have an aluminum vertical element that is 67' tall. I want to
> top-load it on 160 meters and would like to use a three wire approach
> for physical symmetry in support of the vertical element.
> 160? I was guessing about 40' but that was a wild guess.
>
> _______________________________________________
>
>
Charlie remember any top loading connected that far (20') below the top
reduces the over all vertical element height above that point and you will
then end up with a 40' top loaded vertical rather than a 67' foot top loaded
vertical. I would recommend guying with two sets of guying with insulated
material such as Philystran at 40 feet. Put the top loading set from the
top sloping down at an angle (with respect to the
pole) of no less than 45 degrees and no more than 25' where insulators are
placed. (Top loading sloping wires have a point of cancellation if they are
to long or the angle is acute.)
Break up any remaining wires to ground at least every 40-50 feet. You can
get about 10% more top loading by connecting the top three wire spiders
together end to end (inside the insulators) to form a skeleton cone. This
should increase the amount of top loading and bring you closer to 1/4 wave.
These are approximations but if you know someone who can model this you can
have more assurances that what you are putting up will give you the maximum
efficiency at the radiation angle lobe you are looking for.
If the pole is insulated and you have a directed feed the 20 to 30 ohms
resulting impedance, maybe even a bit lower if you have a near perfect
ground, can be matched with an Un-Un or simple L network. If the pole is
grounded you can shunt feed it with a tap about 30 to 40 feet but you will
need to tune out the inductive reactance of the shunt with an ATU.
Remember that resonance is not crucial. What is more important is matching
what you end up with and the ground system this Marconi will need to make it
efficient.
Good Luck with your project.
Herb Schoenbohm, KV4FZ.
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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