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GregS GregS is offline
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First recorded activity by BoatBanter: Jul 2006
Posts: 23
Default How do you make a VHF marine antenna directional?

In article , Larry wrote:
"Denny" wrote in news:1154084481.658770.294700

Notice that mounting a vertical antenna 1/4 wavelength from the side of
a taller tower will cause the metal of the tower to act as a reflector
and therefore the antennas circular pattern will become a cardoid
7.5 dB in a cardioid pattern with all the dipoles on one side of the pipe
(or tower). Download the pdf manuals and have a look.

Sinclair will be there 20 years from now still with a perfect SWR. The one
on our repeater had to be replaced because the 250 mph winds from Hurricane
Hugo blew the top off the building it was on in '89. That's how long the
one that's up there now is...(c; Because the whole thing is a DC short
hooked to the tower, itself, it takes a direct lightning hit to destroy it.
For this reason, you install just the dipoles on the seaward side of the
towers, all in line, without the pipe....about 4' down from the top of the
tower, letting the tower take the lightning hits. That's how we do it at
1800 ft AGL...(c;

Nothing fiberglass survives up there.....

If a vertical is mounted on the tower side, use a top stabilizing rod.

The dipoles can also be staggered to even out distribution however
you want.