[TowerTalk] 80M dipoles/height gain

[alsopb]

Here are some EZNEC calcs of an 80 meter dipole at heights from 60' to
160'

Clearly guys who get even dipoles high win.

height	max gain/angle	half power angles	20deg gain
60'	6.52dbi/89deg	30deg			1.5dbi
80'	6.16dbi/52deg	23deg			2.16dbi
100'	6.38dbi/40deg	19,81deg		3.4dbi
120'	7.05dbi/33deg	16,56deg		5.0dbi
140'	7.84dbi/28deg   14,45			6.8dbi
160'	8.31dbi/25deg	12,39			8.3dbi

The 20 degree angle point was chosen because it represents a point
that the a point in the second peak of the eu arrival angle
distribution with a large fraction of the total . (East coast,
Washington DC) It says going from 80' to 160' one gains about an S
unit in EU from the East coast.

The 6-12 degree region contains the first arrival angle distribution
peak. It takes a dipole at 160' to put much energy there.  A vertical
isn't the answer to cover these lower angles -- unless you have
excellent ground conductivity.  EZNEC shows that verticals are also
poor performers at these angles there in areas of conductivities in
the 2-5 range (my QTH is 2.5.)  Of course, if your vertical antenna is
on a salt marsh, you win.

73 de Brian/K3KO
n4kg@juno.com wrote:
> 
> I would not expect much benefit from a 2L80 at only 85 ft
> which is barely over 1/4 WL high.  The ground reflection at
> 1/4 WL high is centered straight up.  The free space pattern
> of the Yagi is centered at the horizon.  The vector product
> will peak somewhere in between.  You may want to model
> a 2L80 and an 80M dipole at 140 ft and 85 ft and see how
> much net gain you will realize from that configuration before
> proceeding.  You might be surprised to see little benefit
> over a dipole at 85 ft.
> 
> 40M antennas play VERY WELL from 70 to 100 ft so that
> is a good choice.
> 
> Tom  N4KG
> 
> >>>>>>>>>>>
> 
> K7PUC wrote:
> 
> I am planning on installing subject beam at 85' using the Orion 2800
> rotator--both already on hand.
> These 80m yagi posting have me wondering what problems I may be facing.
> My
> plan is to install
> one set of elements on the boom at ground level (crankup tower), raise
> the
> tower to vertical and
> then rotate the boom 180 degrees.  Lower the tower and install the
> opposite
> end elements.
> 
> Never having had a tower higher than 35', I will appreciate all comments.
> 
> BTW, I was mostly interested in a 40m beam but decided to add 80m!
> 
> k7puc
> 
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