Satgen 493  Antennas and Azimuth 6 by GM4IHJ  (BID SGEN493) 1998-09-05

As several readers have pointed out. There is little point in getting
your antenna to point at the right azimuth, if it is way off target in
elevation. So perhaps a few words about elevation alignment , are in
order.

Fortunately for us, earth gravity makes elevation measurement easy .
Using a simple plumb line. Attach a protractor ( as used in school
geometry) to your antenna main element centre support rod, and fix a
weighted line to dangle down from the appropriate point on the
protractor. Then as you elevate the antenna the protactor moves and
the line stays still, thereby indicating the elevation angle. Then you
can compare elevation measured at the antenna with elevation indicated
by your shack rotator to explore the calibration accuracy over a wide
range of elevation angles. After which a further check can be done by
comparing computed solar elevation and with the indicated elevation at
which you get maximum received solar noise.

But is this all there is to it ? No it is not. Your antenna may squint
- a situation which the solar noise check should eliminate. when you
compare mechanical versus radio alignment .

Much less well known , and capable of producing serious misalignment,
particularly if you make small elevation adjustments when using
computer driven auto tracking, is the problem of lack of balance in
the mechanical mounting of the antenna. It is vital if you are to get
accurate tracking that your elevation motion rotates about the antenna
centre of gravity. In far too many amateur installations this truth is
ignored. An out of balance antenna has totally different static
friction characteristics at any one elevation angle compared with
another. So get it balanced ,even if this means running a horizontal
mast member of hard wood or fibre glass through the antenna field just
ahead of the driven element. A situation which is quite normal noting
that the coax feeder going out the back of the antenna is quite heavy
and this puts the antenna centre of gravity someway back from its
halfway point. Naturally it goes without saying that you also keep the
rotator or drive screw for elevation well to one side of the antenna
radiation field.

Elevation drives used by radio amateurs come in two distinct forms -
One of which resembles the azimuth rotator or airscrew pitch motor
driven assembly, or, a quite different and possibly much better type
which uses an elevation screw with good mechanical advantage and
excellent precision pointing properties. This screw form is available
from satTV specialists, and it usually has with it an electro
mechanical or digital readout of shaft position which runs from a grey
code transmitter or similar, on the mast connected via a suitable
length of electric cable so that it can by used on the station 
operating bench.