I am shunt feeding a 5m roof tower against some elevated radials
on 80m. On the top of the tower is a C-3E/A (insulated elements,
each band with its own feeder) & at the end of a further 3m of mast
there is a SteppIR dipole.
For TBDC, I added a 160m radial (there are four 80m radials, plus
a few for 40) & found that by tapping up the mast, I could match
it fairly well on topband. On 80m, the tap point is at the top of the
tower. For caps I use air variables & add doorknobs in parallel
where necessary. Obviously, omega matches are used on both
bands.
An additional 6m or so of wire supported by a pole strapped to the
mast really helped, but once the NE monsoons kick up again, I
am afraid that it will have to come down - though it will probably be
deployed as much as possible from now on... it is clear that the
whole thing is extremely short for the low bands & I need
something more at the top of the mast (perhaps later a scrap R7
base turned up-side-down?).
I need to find a way to feed the tower on 160 without fouling the
tribander. For 80m, the tap is at the top of the tower, spaced
about 30 cm from the tower face & by varying the spacing at the
bottom, better tune it between 75 & 80m. One idea I have is to
use the tribander's boom as the 160m tap & drop a wire from the
end of the boom (either straight back to the tower base, or down
to the roof & then back to the tower base) - this still requires
running up on the roof to work 160, but would make for faster band
switching than what I have now.
Any ideas?
73, VR2BrettGraham
(W6, W7, OH0 & UA4 worked in TBDC with current setup)
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