In article ,
Buck wrote:

I have read several articles that show how this antenna works. The
450 ohm twin lead matches the antenna by wavelength (or some fraction
thereof.) I am wondering if this same concept can be successfully
used with 300 ohm tv twin lead.

Sure, although the actual feedline lengths needed to achieve a match
will be different than would be the case using 450-ohm feedline.

It would be interesting to know if some small contraption could be
made to carry one around for a portable operation successfully.

No doubt. What one would need, I think, would be a set of different
pre-cut segments of feedline (binary powers-of-two multiples of 6",
perhaps - 6" 1' 2' 4' etc.), with preinstalled snap- or screw-together
connectors. Banana plugs/jacks might work but I'd be concerned that
the weight of the feedline might tend to pull 'em apart... something
with screws, bolts, alligator clips, etc. might work better. You
could keep each length of twinlead rolled up and labeled with its
length.

However, I think this might not work out as well in practice as you
might think. If you're operating portable, you'll probably be putting
up your antenna in locations you haven't operated before, with
unpredictable combinations of supports. Differences in the antenna
height, shape (flattop vs. inverted-V vs. bent-all-over-the-place
horror), length, and the influence of ground conductivity and nearby
objects are going to make the antenna's feedpoint impedance difficult
to predict, and thus you may find yourself needing to raise and lower
it several times, and try different combinations of feedline segments,
in order to get an acceptable match.

For multiband portable/emergency antenna use, I'd probably just go
with an as-long-as-practical wire doublet, enough 300-ohm twinlead to
reach the ground from the expected operating height, and a small
T-match tuner with a current balun on the output. Probably less
hassle, quicker to set up and operate, and it wouldn't necessarily
take up any more space than a collection of different-length twinlead
segments with their connectors.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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