Topband: 160 Tower on 80

[Richard (Rick) Karlquist]

On 2/28/2015 5:15 PM, Glenn Biggerstaff wrote:
> 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
> _________________

I have a 90 foot top loaded vertical made from irrigation
pipe instead of R25.  Should be similar electrically.
I have done the voltage feed method on 80 with it, and
it works perfectly.  You just have to have the HV components
and be comfortable with designing a simple matching
network.  If you were using tuned elevated radials on
160, this would make sense because it would relieve
you of having to have a set of 80 meter radials.

If you have normal ground radials like me, you might
want to consider a relay to switch out the top loading
wires.  I currently have an insulated joint at the
60 foot point on my vertical with a relay across it.
When the relay is open, I have a 1/4 wave 80 meter
vertical.  In your case, you would have a 3/8 wave
80 meter vertical, that you could tune to resonance
with a series capacitor.

For details on the relay, see my H&K article:

May 2009 - QST (Pg. 66)
Increasing Relay Voltage Handling Capacity

You should put a string of 10 meg resistors
across the relay to drain static charge.

Rick N6RK