I have been doing much the same here. Faced with a nine inch brick
wall and no windows, I decided not to bring ladderline into the shack.
A "water-cooled" Centaur 4:1 ladderline balun is hung high outside
from a bracket fixed to the wall. Around 20 feet of RG-8 connect the
balun to the TT ATU (the old automatic model 253) through a piece of
polythene pipe built into the brick wall. The antenna is a 40m inverted
V with its feedpoint at around 55 ft. It is fed with a long (80-90 ft)
length of ladderline and I use it on all bands 80-10m. OK; its not
that good on 80m but I have worked VK several times with it. Are there
any snags ?? Yes, I often need to retune when it is raining. Yes,
its definitely not as good as a beam, but it has virtually no
directional properties, so I do not need a rotator.
I even managed to work 210 countries in 2000 with my 10w
Elecraft K2 using the the same antenna. (The K2 now has its own
on-board auto-atu similar to the AT-11).
As antennas go, mine is very crude and I do not need to be
told that it is undoubtedly badly designed/engineered, but it has kept
me on the air for many years now. The SWR on the ladderline and on the
length of coax from the ATU to the balun is anyone's guess, but as
long as all three SWR meters in the line to the 253 ATU indicate well
under 1.5:1, who cares ??
Incidentally, the old 253 tuner is an L-match like the present 238. I
have never used a 238 here, but I would expect it to behave the same
way.
One word of caution. Its not too difficult to homebrew an ATU from
surplus/hamfest components. I have an SPC Transmatch here that I made
old-fashioned style on a metal clad breadboard using scrounged
components. Its breakdown voltage probably far exceeds that of the TT
238, and I used it successfully for years with tube rigs and a 3 x 811A
600w linear. But it is USELESS with my TenTec gear and present antenna
setup. Yes, I can get a match, but if I raise the power level to even
50-100w I have severe RF feedback problems. If I use the TT 253, even
with my Herc II at the 500w output level on 20m where the mismatch is
most obvious, there is no sign of RF feedback.
If you build your own ATU, use a metal box instead of a breadboard.
Also, the conventional Handbook SPC design as intended to cover all
bands seems to have far too much stray L/C to be really easy to use
above 20m. This problem is much worse if like me you use physically
humongous components.
Anyway, you can probably buy a 238 for what it costs to get really good
parts for an SPC and then build it into a screened enclosure. Why make
problems for yourself ??
John G3JAG
On Tue, 30 Jan 2001, Frank Holladay wrote:
> I have used an external 4:1 balum mounted just outside the shack for years
> with ladder line to the antenna. If the coax is kept short ie. less than
> 10-15' and is of good quality, the added loss will be minimal.
> 73,
> Frank K4VMO
>
>
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