Hi, Glenn
There's a lot to be said for Rich's approach if you can manage the
additional tower. It does need to be well separated from the 160 tower as
some interaction is likely. You might want to do some modeling in EZNEC
before installing the additional tower. Still phased, or parasite arrays can
provide substantial results for 80 and 160! I built a large 5- element
steerable array for a friend for 80 meters. It had a central 1/4 wave GP
radiartor and 4 surrounding GPs that could be switched between reflector and
director tuning with stubs of ladder line that could be remotely shorted
with relays to achieve different directions. It was a KILLER antenna for 80
and 75 meters and Jim didn't wait fr anything!! - Even to breaking EU
pile-ups for A61 with ONE CALL from Virginia!! It was a HUGE success!
So, some variatiom of Rich's approach might well have merit! I would
strongly recommend some advance modeling and experimentation with EZNEC
before installing the second tower. I have thought of putting an 80m trap
in the top horizontal wire for my inverted L, but I didn't like the idea of
an 80 m trap 70' in the air. So I elected to add a 2nd vertical radiator for
80m and feed it in parallel with the 160 inverted L. That's also an option
for you, if you add an 80m radiator in parallel and run it up the side of
your tower. If you are using elevated radials, you[ would need to add an
additional set for 80m.
Anyway, GL and have fun!
73,
Charlie, K4OTV
-----Original Message-----
From: KL7RA [mailto:kl7ra@ptialaska.net]
Sent: Saturday, February 28, 2015 10:53 PM
To: Charlie Cunningham; 'Glenn Biggerstaff'; topband@contesting.com
Subject: Re: Topband: 160 Tower on 80
>Any thoughts or alternative ideas would be greatly appreciated.
>Glenn WW4B
Hi Glenn, all of Charlie's, K4OTV ideas work of course but you did mention
alternate ideas. I also have a Rohn 25 insulated base tower that is 142 feet
to the top of the stinger that I use for 160.
By far and the easiest solution 100% guaranteed to work for a clean switch
from 80 to 160 is a second tower some distance away. Used 25 is relatively
cheap and Philly now is sold by a lot of folks. The only switching is in the
shack, etc. Simple is good.
I chose not to use the 2nd tower as a vertical and it supports a 4 square
using the DXE hybrid. For the radiating elements I used dipoles with shield
end sharply folded back to the tower. Because the elements come pretty close
together at the top you do lose a little gain but not that much over
verticals and verticals require a lot of radials where this array just has
the one element folded back for each direction.
This array seems to work so well I build another for 40 meters under a full
size 40 Yagi. At times the Yagi is better as expected but the ops here like
the instant switching and use it a lot.
Added bonus these arrays survive the winter storms here with
100 mph + winds.
73 Rich KL7RA (now on topband but no one can hear me yet.)
> Well, Glenn, I would lean toward voltage-feed at the base, since you
> have that insulated tower! Because of the lower current, the
> ground-losses would be minimized, and the current maximum would be
> fairly high on the tower, resulting in a nice low-elevation angle,
> omni-directional radiator for long haul 80m DX work. Of course you
> would need a robust tapped parallel LC network with a robust inductor,
> probably mad of copper tubing and a really high voltage air variable
> capacitor, or better, a vacuum variable and there would be some
> substantial switching challenges to switch the feed between 80 and
> 160, that would be avoided with your trapped top loading approach, but
> full-power 80m traps 90' in the air are non-trivial components also!
> I LIKE the voltage-fed 1/2 wave vertical approach and have had
> wonderful success with it on 40m, where I fed the vertical 1/2 wave
through a 1/4 wave 450 om line for an almost perfect match!! Great antenna.
> And I used it as the driver for a wide-spaced 3-element vertical 40m
> yagi for Peter 1 Island and Bouvet and it was a killer antenna for SE
> Asia on the evening LP.
>
> So, that's my $0.02! If it were me, I'd leave the top-loading alone
> and do the work to voltage feed that insulated tower! Should be a
> great antenna for both 80 and 160, and has the advantage that all the
> tinkering and tweaking can be done at ground level!
>
> GL and have fun!!
>
> 73,
> Charlie, K4OTV
>
>
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of
> Glenn Biggerstaff
> Sent: Saturday, February 28, 2015 8:16 PM
> To: topband@contesting.com
> Subject: Topband: 160 Tower on 80
>
> Hi all, I have a 90 foot Rohn 25 tower with an insulated base and
> insulated guy wire sections for top loading ,base fed for 160 meters.
> It work great ,but I would like to use it on 80 meters as well.
> The 3 ideas I have considered are voltage feed at the base with a
> resonant LC network at the base, but I am a little worried about the
> voltages present at legal limit power. Second idea,disconnect the top
> loading and put a trap between the top loading and the tower to
> divorce the top loading on eighty then an L network at the base for
> 80. Third idea, run a wire as a sloper either a quarter wave fed
> against ground or a 1/2 wave dipole from the tower.
> Any thoughts or alternative ideas would be greatly appreciated.
>
> Glenn WW4B
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