Pointing Calculator

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PALAPA-C2 Commercial communications satellites are geostationary, and therefore have orbits which live in the equatorial plane, during the spring and fall equinoxes, the sun also passes through this plane. As seen from the ground, the sun seems to pass behind the satellites once per day. During the time when both the satellite and the sun are in the ground station's field to view, the RF energy from the sun can overpower the signal from the satellite. It is the loss or degradation of communications traffic from the satellite that is referred to as sun fade, sun transit or sun outage.
The duration of the sun outage depends on several things such as : the beam width of the the field of view of the receiving ground antenna, the apparent radius of the sun as seen from the Earth (about 0.25 deg), the RF energy given off by the sun, the transmitter power of the satellite, the gain and S/N performance of the ground station receive equipment, and other factors. All this can be used to determine the outage angle of the receive antenna. Outage angle is defined as the separation angle (measured from the ground station antenna) between the satellite and the sun at the time when the sun outage signal degradation begins or ends (see below)


Also, due to the many differences in ground station equipment, some stations may experience a complete loss of signal while others may only experience a tolerable degradation of signal. This makes the determination of antenna outage angles difficult without complete

information about the ground station equipment. For this reason, the following approximations were used to generated the antenna outage angles attached later

Antenna outage = half the 3Db beamwidth + apparent radius of the sun
Where Freq = Downlink Frequency in Ghz ( 3.95 for C-Band and 11.95 for Ku-Band ), Diam = Dish diameter of ground station receive antenna in meters.