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Old May 12th 07, 01:48 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Long inverted V not working well, why?

Rick (W-A-one-R-K-T) wrote:
Seems very strange. Any ideas that might account for why the V doesn't
work better?


The key is the combination of feedpoint impedance and
length of the ladder-line. Some lengths of ladder-line
at some frequencies are close to worst case. For instance,
if the feedpoint of the 160m dipole is 6000 ohms on 75m,
you certainly don't want to feed it with 1/2WL of
ladder-line on 75m.

The free demo version of EZNEC available from eznec.com
will probably tell you what is wrong with your installation.

There's a DOS program on my web page that will tell you
the optimum lengths for feedline. It can be downloaded
from http://www.w5dxp.com/imax.exe

For instance, with a 260 foot dipole used with 450 ohm
ladder-line on 3.8 MHz, the optimum feedline lengths
are ~55 feet and ~172 feet. If your feedline length is
halfway between those two lengths, i.e. ~113 feet, it
is a worst case impedance situation for 3.8 MHz.
--
73, Cecil http://www.w5dxp.com
 
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