[TowerTalk] Takeoff angle
rxdesign at ssvecnet.com
Mon Jul 24 09:06:25 EDT 2017
I'd agree if giving a presentation to potential neophytes, which I did to a
local club on the use of HFTA, one should be careful to point that there ARE
signals, lower in level, below (and above) the peak.
However its my assumption that is understood by those here. I'm not nor I'd
hope is anyone thinking that all other angles are excluded. But it is in
knowing where the peak is that one can see in their 'minds eye' how the lobe
might fill in above and below it.
From: Jim Brown
Sent: Monday, July 24, 2017 12:17 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Takeoff angle
I consider use of the words "takeoff angle" to be VERY misleading, and
cause a LOT of misconceptions. It is common to use the words "takeoff
angle" to define the vertical angle at which field strength is greatest,
and that the antenna only works at that angle. Nothing could be further
from the truth.
Several years ago, I presented a modeling study showing that the low
angle radiation (15 degrees and below) of a horizontal antenna for 80 or
40 M continues to increase as the antenna is raised above ground. I
showed this by ignoring where the peak of the vertical pattern was,
instead looking only at the low angle field strength as the antenna was
raised. I didn't look at the SHAPE of the pattern -- instead, I plotted
curves of field strength at 5, 10, and 15 degrees as the antenna was
raised. A similar study for 20M produces comparable results, taking
wavelength into account. That study is presented in the link below,
starting around page 10.
That study is, of course, for "flatland," where terrain is not a factor,
but the same concepts apply in irregular terrain, except that the
terrain shifts the lobes up and down.
73, Jim K9YC
On 7/23/2017 6:27 PM, Steve Maki wrote:
> Err, we better keep straight whether we're speaking of heights above
> ground or takeoff angle.
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