Hi Art,

A few points below, but first just remember that the TOA of any
horizontally polarized antenna is primarily a function of ground
reflections which vary according to height above ground. Previously
you mentioned that your antenna was designed for a TOA of 10 degrees.
That cannot be true except for a specific height above ground. Whether
Yagi, Quad, Log, Rhombic or any non-vertically stacked antenna.
Something like a Sterba curtain is different because it has multiple
elements stacked vertically which CAN be steered by phasing.

art wrote:

yes it is twenty meters and I am
located in the couintryside that I understand is the highest between
Chicago and New Orleans and since this is the bread basket of the U.S
the ground loam is excellent.

1. Absolute height above sea level means nothing. What is important
to TOA is your relative height above the terrain within a mile or two
of your tower. I operated from Colorado for ~30 years and always got a
chuckle from the guys who said, "My antenna is over 1 mile high". In
fact what is important for determining TOA is not height above sea
level but height above surrounding terrain.

2. Ground conductivity has minimal effect on horizontally polarized
ground reflections. You may be thinking of vertically polarized
antennas like verticals where it has a huge effect. HFTA does have
conductivity as an input parameter but it has minimal effect, at least
in my case (average ground versus salt water).

I use 7/8 andrews plus a long length
underground and the tower is hinged in two places
as well as another one for array tilting.

Phsical tilting has minimal effect on the ground reflections for the
angles of interest (4-10 degrees) because the vertical lobe is not very
narrow (typically a Yagi has ~50 degree 3 dB vertical beamwidth). In
other words tilting has a far secondary effect on TOA versus changing
the antenna height. You can prove this to yourself by modeling with a
program like EZNEC (HFTA does not allow tilting because it is
physically impractical and has little effect).

Pretty simple question for
those who know the answer after all you start off with 3 db gain in two
different directions thereffore it would seem to me that a yagi was
only 50% efficient

I believe you're referring to a dipole which has 2+ dB gain over
isotropic in the two directions broadside to the element. If we add ~6
dB from ground reflection gain, we get 8 dB gain over isotropic, but
this is ONLY for a specific TOA which is determined by the antenna's
height above ground. Of course a good Yagi will typically have 25-30
dB Front to Rear, so its backward lobe has very little of the total
energy (far less than 50%).

Bottom line to all of this is that your antenna's height above ground
has the primary influence on TOA. The only other way to "steer" the
vertical lobe is to mount your antenna on a motorized tower (unless you
go to vertically stacked elements and phasing).

Put your single antenna at 120' and the vertical pattern will be
centered on about 9 degrees (assuming flat terrain).

73 & GL!

Bill W4ZV

P.S. Here are some results using HFTA for my 10 meter 3-stack:

http://users.vnet.net/btippett/terrain_&_toas.htm