Bob, it is almost a certainty that you need to tap the tower much lower.
I just finished helping a friend tune his 65 ft aluminum tower for 160.
He has a TH6 on top. Our first tap was too high but still well below the
top and the swr was about 2. The next try was lower and it tuned right
in below 1.5 with a gamma match. I don't have a number for the tap point
but believe it was about 2/3 up. You did not give details on your
crankup. I have a 131 ft UST with a 6 el 20 on it. I tap it half way up
with a 3 ft extension to one of the coax arms and a nr 10 wire to the
ground. It gamma matches to 1.2 swr. I would think you could lower your
tower and use an extension ladder to tap the tower for an arm at the top
of one of the sections. How about using a couple of pieces of the
plumbers galvanized pipe strapping around the top of one of the tower
legs. This is the stuff with the 1/4 inch holes in it. If properly
placed you should be able to find a spot where it does not rub as the
tower is raised and lowered. Another possibility is to drop a couple of
pieces of galvanized all thread rod down the top of one of the sections
corner posts. You could hack saw a slot in it and bend it out until it
is a force fit.
73, Dan, N5AR
Bob Henderson wrote:
>
> Forgive me, I know this subject has cropped up several times here. I am
> hoping someone among you tower-talkians can give me some guidance on what my
> next move should be.
>
> I have a crank up tower which is about 65ft fully extended, on top of which
> I have 18ft of HD stub mast. At 65ft I have dipoles for 160m and 80m, at
> 67ft a F12 C31XR, at 76ft a Cushcraft XM240 and at 85ft a 5 ele 6m yagi.
>
> I am trying to shunt feed the tower for 160m. As I want to retain the 80m
> and 160m dipoles at this stage, I have fitted each of them with decoupling
> traps resonant at 1830 kHz. I have dropped a shunt wire from 65ft at a
> distance of 30 inches from the tower.
>
> Results so far:
>
> The lowest SWR I can get at 1830 kHz is 2:1, which I get with 225 pf of
> series capacitance.
>
> The frequency on which I can get my minimum SWR of 1.3:1 is 2220 kHz with a
> series capacitance of 100 pf.
>
> Bringing the shunt wire closer to the tower brings down the frequency at
> which I can get minimum SWR, however the minimum SWR increases as I go away
> from 2220 kHz. I have tried a shunt capacitor and this produces roughly the
> same effect.
>
> At this point I am unsure whether to reduce shunt height, alter shunt
> spacing or attach some light weight alloy tubing to the top of the stub mast
> to increase overall height. Perhaps I will need to do all three?
>
> Every time I need to make an adjustment I have to crank the tower down, luff
> it over and partially dismantle my C31XR and XM240 so I can reach the parts
> I need to adjust. As you will understand, I'm rather keen to minimise the
> number of times I have to do this.
>
> Words of wisdom gratefully received.
>
> 73
>
> Bob 5B4AGN, P3F
>
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