On Mon, 28 Sep 2009 18:42:34 -0400, Tommy wrote:
>I believe the objection was to your comment: " Open wire line is
highly
>over-rated.." to which hardly anyone agrees.
Because its virtues have been preached for so many years in the ARRL
Handbook and Antenna Book. Science is not a matter of opinion, but of
fact. Open wire line (and window line) are wildly over-rated, because
they are preached as a one-size fits all solution. They are NOT!
Because it cannot be choked, any imbalance in the antenna system makes
ANY feedline radiate (and receive). This happens whether it's coax or
a so-called balanced line, BECAUSE of antenna imbalance. The virtue of
coax is that you can choke it to kill the radiation. The shortcoming
of balanced lines is that you CANNOT choke them effectively.
It doesn't take much to make an antenna unbalanced -- ground slope, or
the antenna slopes, or one end is close to a building or tower or tree
and the other is not, or the two sides of the antenna are of unequal
length.
This is a big deal if you live in an urban neighborhood, with noise
sources all around you. We have few weapons in this fight, and two of
the most important are 1) antenna directivity and 2) moving the
antenna further from the noise source. A feedline that radiates (and
receives) defeats both of those weapons.
73,
Jim K9YC
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