Here are some EZNEC calcs of an 80 meter dipole at heights from 60' to
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
> 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.
> plan is to install
> one set of elements on the boom at ground level (crankup tower), raise
> tower to vertical and
> then rotate the boom 180 degrees. Lower the tower and install the
> 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!
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