TopBand: vertical and inverted vee interaction
Thu, 18 Mar 1999 09:48:15
>Will the inverted vee degrade the vertical pattern?
It certainly will but it is really hard to say how much since
each case would be unique. I had a dipole at 145' and a vertical
GP about 50 feet away. The resonance of the GP would shift from
1830 to about 1900 just when switching the dipole at the
top of the tower. This was actually not all bad for me since it
was an easy way to change the GP resonance to the JA window! The
antennas seemed to operate independently since they were mostly of
opposite polarization, but there was still noticeable interaction.
One of the best ways to isolate an inverted-vee from a shunt-fed
tower is to use a Resonant Balun which eliminates common-mode currents
and decouples both sides of the wire antenna. At last year's 160 BBQ
at K9RJ's (W9DXCC gathering), Jim K9RJ gave me a paper he wrote
for inclusion in ON4UN's new book. He claims no change in the
feed-point impedance of his shunt-fed tower when the inverted vee
is connected. The top loading effect of the wire antenna and the heating
effects encountered with conventional baluns were completely eliminated.
Jim is a member of this reflector and he might be willing to send you
a copy or you can wait for ON4UN's book which should be out soon.
73, Bill W4ZV
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