TopBand: Re: Rohn Tower on 160m

[Jim Henderson]

Phil, Earl, and reflectees:


>Because Rohn 25 comes in 10' lengths, this posed somewhat of a dilemma --
>using 120' of tower requires 13' of 2" mast above it (total height =
>133') to resonate at 1830 kHz.
>
>Using 130' of Rohn 25 without a mast resonates too low in frequency --
>128' of the tower will resonate at 1830 kHz, and I'm sure you don't want
>to cut 2' of tower off.
>

        An additional thought: I used the Rohn 3-foot top bearing shelf, a
pair of non-Rohn thrust bearings, a 18-aluminum 2" mast,and a ground strap
(on 80m). I mounted the 2 bearings on the shelf, slid the tube thru them,
and set the total length to what I roughly calculated (before NEC!). I used
a hose clamp to secure the ground strap to the mast, and the strap was
bolted extremely well to the top plate. I did this to secure a better RF
joint than the bearings gave.
>        It was easy to then tune the antenna by sliding the mast in/out of
the bearings. 

        The bent corners and holes in the top plate made it easy to also
build a capacity hat so I could then try using a top loading coil to tune
160m. 

        It worked pretty well on 80m, and I had a very small BW on 160m
nder 2:1 VSWR. But because I could not put out an extensive ground system
in our high-loss desert soil, I was never happy with it, and switched to my
present "African Marconi" 1/4 slopers. 
        
        BTW, with these and 100 watts, I worked all the usual EU/PAC
stations on topband; and last season, with 400 watts worked the 9X4WW,
ZS4TX, and the /V51 boys.

        After all the work on the tower vertical, which I think worked much
etter than any other vert I had here, I found I had built a better
mousetrap where what I really needed was a cat, hihi.

        Much good luck with your vertical.

73 de Jim, KF7E
ex: 5X1XX, 7Q7JH, ZM7AH, ad nauseum...




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