Fw: [Towertalk] Re: Comparison!!

Mon, 15 Jul 2002 18:18:18 -0700

Gary is right-- visualize a BIG DOUGHNUT over your vertical.
make is of no concern, as all gain verticals operate similary!
your radiation pattern will be with most power concentrated on the horizion,
with 3 dB down points at aprox 10-15 degrees over and under the horizion,
decreasing to 20-30 dB below max at space directly above/below  your
antenna. Big problem with "omni gain ants" is that in order to get the extra
gain on horizon, must take away from other directions !  that at elevations
above the horizon are most likely wasted radiation  is understood, however,
BELOW , is NOT!
may find an inverted groundplane  (driven element BELOW the ground radials,
in parallel,  will keep your close end coverage, while going for max umph on
horizon!  worked for railroad for years, biggest problem is water going down
the mounting tube for the upside down ground plane !  as info, jim nn7k

Gary sent:

 As we discovered years ago using the StationMaster-series of
> antennas, the antennas performed remarkedly when placed at a high-profile
> site...  ~ 600' AAT.  Our usable coverage area expanded considerably.
> Unfortunately, mobiles within 10 miles of the xmtr site couldn't access
the
> repeater!  The high gain of the antenna created a null (or loss of signal)
> in the area immediately (below)surrounding the site.  The antenna was
simply
> "overshooting" nearby stations.  The signal was maximized for the horizon.
> The textbook solution to this problem was to mount TWO antennas... one
> upside down just below the 'top' antenna.  This takes advantage of the
> radiation angle of the main lobe.
>
> I mention this as "food for thought".  Perhaps you already thought of this
> and have planned accordingly.  Perhaps it doesn't apply.  BTW... we also
> used split antennas to compensate for this and other problems, such as
> 'desense':  xmit antenna low and rx antenna high.
>
> GL
>
> gary b
> k3gb
> RVN BTO
>
>
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