Antenna Pointing Angles - Advantech AMT-73 Installation And Operation Manual

This single orbit has to be used because it is the only one where the G force generated by the speed a
satellite needs to travel at to match the earth's rotation equals the gravitational pull of the earth. Any
other orbit and the satellite would either crash to earth or fly out into space.
The direction an antenna must point in order to receive the signal from a given satellite is determined
by the antenna's location north or south of the equator and the position on the equator over which the
satellite is located.
A satellite's position is given in degrees of latitude and longitude in the same manner as a position on
earth.
Latitude is measured in degrees north or south of the equator which is at 0 degrees latitude. The
range is from 90 degrees north via 0 to 90 degrees south. For example, London UK is 51 ° 32' north
and Sydney Australia is 33 ° 55' south. Since any geostationary satellite must be over the equator its
latitude is always zero degrees.
Longitude is measured in degrees east or west of the Prime Meridian. The Prime Meridian is at 0 °
longitude and is an imaginary line running north/south on the earth's surface from the north pole to the
south pole and passing through the Greenwich Observatory in England. All other points in the world
are either east or west of this line. There are 360 ° of longitude expressed as 0 ° to 180 ° east and 0 ° to
180 ° west. 180 ° E is the same location as 180 ° W and this position is the International Date Line. For
example, Sydney Australia is at 151 ° 10'E whereas Washington DC USA is at 77 ° 00'W.
The latitude of a satellite is the same as that of the location on the equator directly below it.
For the purpose of calculation, latitude and longitude are represented as decimals. The sign of the
decimal is used to distinguish North (positive) and South (negative), and East (positive) and West
(negative).
So for the above examples:
Latitude (London, UK):
Latitude (Sydney, Australia):
Longitude (Sydney, Australia):
Longitude (Washington DC, USA):
A.2.5 Antenna Pointing Angles
The Azimuth and Elevation angles along which an antenna must point to receive a particular satellites
signal can be calculated. The information required for the calculation is the location, in latitude and
longitude, of the antenna and the longitude of the satellite. Three calculations are required, one to
calculate a value to be used in the Azimuth and elevation calculations.
The formulas are:
=
d
Elevation
Azimuth
AMT-70/AMT-73/AMT-75 Installation and Operation
51 ° 32'N
33 ° 55'S
151 ° 10'E
77 ° 00'W
(
+ − ⋅ ⋅ ⋅
2 2
s e 2 s e cos( a
⎛ − −
2 2
s e d
= − ⎜ ⎜
1
sin
⋅ ⋅
⎝
2 e d
⎛
⎜
−
= ±
1
180 tan
⎜
(
⎝ cos Elevation
+51.53 °
-33.92 °
+151.17 °
-77.00 °
)
⋅ −
) cos( b c )
⎞
2
⎟ ⎟
⎠
( )
⋅ −
s sin b c
)
⋅ − ⋅
2 2
d s sin
⎞
⎟
⎟
( )
−
b c ⎠
135