I would want to see a terrain analysis, e.g., the effect of your terrain on
the idealized pattern of your 40 meter antenna.
But in general, the 70 foot height suppresses high angle radiation, and has
a single pronounced lobe at the low angles. Another poster commented on a
stronger signal at 95 feet later in the opening.
Using my terrain toward NE, I get the following with a 2 el yagi at various
heights using TA.
height main lobe high lobe
66 11.8 Dbi 29-32 deg none
72 11.9 Dbi 26-30 deg none
78 12.1 Dbi 23-27 deg -3.8 Dbi 77 deg
84 12.3 Dbi 23-26 deg 0.3 Dbi 77 deg
90 12.4 Dbi 22-25 deg 2.9 Dbi 75 deg
The absolute value of gain varies greatly with the antenna and ground
I'm not sure that the 0.6 dB difference between 66 & 90 feet would account
for David's observed difference in performance. The higher angle at 66'
would seem to make it better *later* in the opening.
In my upcoming installation, the 3 el 40 will be at 73 or 81 feet depending
on tree tops.
One of the considerations is the elimination of the high angle lobe for
rejection of stateside signals on receive.
From: email@example.com <firstname.lastname@example.org>
To: email@example.com <firstname.lastname@example.org>
Date: Wednesday, March 03, 1999 3:00 PM
Subject: [TowerTalk] 40m Yagi @ 66' vs 92'
>I currently have a 89' US Tower, which I usually park at 80' for greater
>strength ... less stress on me :-) .... with a KT-34XA at 81' and a
>2 el shorty 40 at the mast top at 92'. I'm contemplating some antenna
>changes which would necessitate putting the 40m yagi on a ring-rotor on
>the fourth tower section at approx. 66' up. Modelling and gut-feeling
>tell me that I probably wouldn't notice a DISCERNABLE difference in
>performance because the 40m ant really wasn't high enough to be working
>optimally to begin with.
>Does anyone have any experience with actual/perceived performance
>differences at these height differences ? All comments appreciated..
>Wayne - W9II email@example.com
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