Topband: 160 Tower on 80

[KL7RA]

>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 at contesting.com] On Behalf Of Glenn
> Biggerstaff
> Sent: Saturday, February 28, 2015 8:16 PM
> To: topband at 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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