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Re: [TowerTalk] Tower as a Vertical

To: "Daniel Hileman" <>,
Subject: Re: [TowerTalk] Tower as a Vertical
From: "Dan Zimmerman N3OX" <>
Date: Sun, 11 May 2008 11:10:05 -0400
List-post: <">>
> Second,I am thinking about a full size 75m vertical out of difficult 
> would that be to do?

Not hard.

>Could I get a 20' "mast" out of the to make up the difference in
height needed for a full size >radiator??

Sure, a 20' tapered aluminum radiator would do it.  I wouldn't add
more tower if I were just using it as a vertical.  Of course, if you
install it right and end up with 60 feet of properly installed and
guyed 25G, you  might want to put something on TOP of it ;-).
Honestly, I bet even 45 feet with a  tribander or even a rotatable
trap dipole  on top is starting to approach resonant on 80m but I am
not really sure.  However, it's a common practice to use the whole
tower and rotatable antenna on top as a vertical, top loaded radiator
on the low bands.

>(DO I EVEN HAVE TO INSULATE IT?? I have a friend who built a NON
insulated 160m >Vertical.) PROS, CONS???

No, you don't have to insulate it.  Pros: no $400 insulators (these
things have to be pretty strong).  Cons: harder to multiband.  "Shunt
feeding" a tower involves a gamma match which needs to be set for each
band.  People have multibanded shunt feed towers (80/160) by switching
the gamma matches with vacuum relays and so forth.

> Third Question: Can I  make it multi-banded? Like just use a tuner on 160-10M?

This is where it's easier (maybe totally necessary) to use an
insulated tower... and I use 60 feet of radiator on 160 thru 30m with
good results. Higher in frequency than 30m, the vertical  starts to
act as a longwire that fires UP ;-)  It's a gradual process, but you
start to get a lot more high angle radiation and less down at useful
communications angles.  My 60 footer generally has pretty good signals
coming in on 20m though when I select the 30m matching network... not
as good as my 20m Moxon but if I had a matching network for 20 it
would probably be occasionally useful when I don't want to swing the

But if you're going to do 60 feet as a multiband radiator, you pretty
much have to insulate.  On 40m, for example it's pretty much an end
fed half wave which I've had great success with but you can't ground
the base of one of those!

I much prefer high-ish horizontal antennas on 20m and up so I haven't
chased after a single-vertical homebrew solution over all of HF
before... but the 60 footer works great and probably quite a bit
better than totally commercial offerings on 30m and down.

But like you've noticed, the insulators can get pricey.  I think
there's certainly a crossover price where you might decide to ground
the tower, use it just on 160m and 80m, and use it to also support an
inverted vee doublet fed with ladderline or something for 40m and
up... or some other antenna for the higher bands.    For less the cost
of the insulators you found, you could even devise a vacuum relay
switching arrangement where the doublet was used as top loading on the
45 foot tower for 80/160 and used as a doublet to the tuner on the
higher bands.

One other thing:  to use a 65 foot radiator on 160m effectively you
need to load it efficiently, and I don't think a commercial tuner at
the base will do that well.  It will be pretty stressed to try to
cancel all that capacitive reactance, so adding a dedicated loading
coil on 160m is probably a better bet.  At low power a beefy tuner
might be survive, but matching such a low resistive part and such a
high capacitive reactance is likely to cause quite a bit of loss and
possibly smoke the tuner depending on how much power you're running.
A legal limit tuner run at 100W power level should survive ;-)

I've been very happy on 160 with a 60' wire base loaded with a big
coil ( but I'm
on the extreme East Coast with nothing to compare it to ;-)


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