Let's get on the same page regarding parallel wire feedline terms
first. Balanced line usually takes three forms:
Window line: the brown plastic stuff, 450 ohms nominal, with punched
out rectangles in between the conductors.
Ladder line: Looks like a tiny rope ladder; conductors spaced apart 3
to 6 inches using ceramic dowels, or other material such as plastic
irrigation pipe as spacers.
Open wire line: parallel conductors at a fixed distance apart and
held taut so no spacers are needed.
I don't recommend window line; the other balanced line types work
better. If your open wire feeder is what I call an open wire feeder,
then you're all set on that one. The Matchbox is a fine balanced
network. You don't need any kind of balun or unun with it, because it
is essentially a variable balun on its own. the link and coil are a
balanced to unbalanced transformer.
I recommend continuing with this and if possible, doing away with the
hassles of a remote tuner by continuing the OWL right to the building
where your shack is, and coming in via parallel feed throughs, with
the Matchbox positioned on a shelf just inside the shack wall. Then
you can run unbalanced line to whatever gear you are using.
The single dipole fed in the center is great, but for 20 m. and above,
consider a second dipole, 1/2 w. on 20 m. for use on 10 to 20. Locate
it somewhere so it is at a right angle to the low band dipole. The
matchbox will provide a match to a 50 ohm line on all bands, even 12,
17 and 30 m. Be sure to ground the matchbox. I put brass banana
jacks on my outside feedthroughs, and brass banana plugs on my ladder
lines and switch feeds by simply plugging and unplugging line and it
makes a good disconnect for thunderstorms. The reason for the 1/2 w.
dipole on the high bands is that it provides a more predictable
pattern. An 80 m. dipole can work on 10 m. but the pattern will be
lots of lobes going off in a lot of directions.
Balanced line for balanced antennas.
Unbalanced line for unbalanced antennas.
73
Rob
K5UJ
<<<I spent some time trying out various wire antennas at the summer cottage and
have more or less settled upon a dipole antenna fed with a short length of open
wire feeder that runs from the antenna feed point to slightly above ground
level, the open wire feeder is in turn connected to a Johnson match box (a
tuner with a balanced line connection), which in turn feeds a coaxial cable
that runs to the radio. The tuner sat on top of a short step ladder during my
tests.
The coaxial cable had various mix 31 and mix 43 ferrite chokes applied. It all
more or less worked as I expected it would on various bands.
Moving forwards I'd like to replace the Johnson Matchbox with an auto tuner.
At this point I'm leaning towards purchasing a suitable Balun from DX
engineering, connecting that to the output of my SGC231 tuner and replacing the
Johnson Match box with the Balun and the auto tuner.>>>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|