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) |
