[TowerTalk] New Tower/Antenna Installation

[Guy Olinger, K2AV]

What most of them are doing is responding to figures like these for a 3
element 40 over good flat terrain:

100   5.7   10.7   12.7   13.0 @ 18.5 d
090   4.8   10.0   12.2   12.9 @ 20.0 d
080   3.9   09.2   11.6   12.7 @ 22.5 d
070   2.8   08.2   10.7   12.4 @ 25.5 d

The particulars for a given height and gain might change with antenna,
but the SHAPE of these figures will remain the same. It IS true that
there is a nasty high angle lobe at 100 feet, which can let in a lot of
stateside QRM, maybe 15 dB difference between 70 (least) and 100 feet
(most local reception). But the gain at five degrees above the horizon
changes almost a dB per 10 feet !!

HOWEVER, this does NOT apply if the terrain is gently rolling down
toward the desired direction. Such a favored location is HOT STUFF at 5
degrees almost regardless of height, and BETTER at 70 feet overall.

It's really not such a simple question. More if you are interested.

- - . . .   . . . - -     .   . . .     - - .   . - . .

73, Guy
k2av@contesting.com
Apex, NC, USA

----- Original Message -----
From: Paul Christensen <paulc@mediaone.net>
To: <towertalk@contesting.com>
Sent: Wednesday, May 10, 2000 11:24 AM
Subject: [TowerTalk] New Tower/Antenna Installation


>
> I am considering the purchase of a Force12 40-meter monoband MAG 340N
and
> multiband C-31XR antennas to be mounted on either a Tri-Ex Sky Needle
or
> LM-series 70-foot tower.  Apparently, the new MAG 340N is resistant to
> mutual coupling effects and can be mounted within a reasonably close
> proximity to multiband Yagi antennas on a shared mast.  With this in
mind, I
> would like to mount the MAG 340N on top of the C-31XR by a distance of
15
> feet, both pointing in the same azimuth.  My question concerns the
height of
> the antennas and specifically, given the constraints of a single tower
with
> these two antennas, is there an optimum "overall" height for the
40-meter
> antenna?  I want to place as much emphasis as possible on the 40-meter
> operation.  It would appear that the "optimum" height for 40-meters is
a
> half-wave above ground in order to minimize the effect of high-angle
lobes.
> However, I see many single 40-meter monoband antennas mounted up to
100-feet
> above ground.  Why, if more high-angle lobes are produced?  I realize
the
> ideal situation is to incorporate more than one level of stacking, but
I
> want to stay with one antenna at a "best overall" height.  Thanks!
>
> -Paul, W4XR
>
>
>
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>


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