[TowerTalk] 120' 160m vertical

[K4SAV]

I would expect that 120 of Rohn 45 with a three element 40 meter Yagi on 
top to be resonant somewhere around 1.6 MHz.  Since it is so tall, if 
you match it with a series cap, the feedpoint impedance will probably be 
too high, maybe about 80 ohms.  I suspect that you will need a two 
element matching network.

Also if that 80 meter four square is made from bent vertical dipoles 
with the feedlines going over to the tower, you will need to add some 
good chokes on the feedlines to keep the dipoles from loading the tower 
and moving the resonant frequency even lower.

I would recommend modeling this to make sure the tower isn't going to 
mess up the four square.  You do have a lot of freedom in changing the 
tower's resonant frequency since it is floating, but a model would alert 
you as to what to expect. I think this should work well if done correctly.

Jerry, K4SAV

Mark Robinson wrote:
> Thanks for all the help on the series rf caps. I am thinking of putting up a 
> 120 foot Rohn 45 tower which is insulated at the bottom, so that it becomes 
> a 1/4 wave vertical. I would like to feed this tower with a series cap for 
> 160m operation provided I have enough top hat effect the beam mentioned in 
> the next sentence. I would like to put a 40m beam on the top and hang 4  80m 
> four dipoles off the tower configured as a Comtek 4 square . Will all this 
> play together or am I missing something. I am not sure how the 40m beam will 
> play on a "hot" tower.
>
>
> thanks  Mark N1UK
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> _