Sun Outage Problem in Satellite TV Channel

Sun Outage or Sun Transit or Sun Fade
Geostationary satellites are fantastic means of communication except for one little problem called sun outage or sun transit or sun fade. It is an interruption in or distortion of geostationary satellite signals caused by interference from solar radiation.  Because the sun is a powerful broadband microwave source and has a noise temperature. The elevated temperature of the sun causes it to transmit a high-level electrical noise signal to the receiving systems. For that reason when the sun passes directly behind the satellite (when viewed from earth) that means the sun is in direct line with a communication satellite,  reception of the relatively weak satellite signals is affected. 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.

Figure: Graphical representation of sun outage problem.

A most common video on sun outage problem

When it Occur
A sun outage typically occurs around the time of the equinoxes. This natural  illusion happens twice a year when a satellite and a receiving earth station come directly in line with the sun. In the northern hemisphere, sun outages occur before the March equinox (February, March) and after the September equinox (September and October), and in the southern hemisphere the outages occur after the March equinox and before the September equinox. The sun radiates strongly across the entire spectrum, including the microwave frequencies used to communicate with satellites (C-band, Ku band, and Ka band). So the sun swamps the signal from the satellite.

How long do they last?
For geostationary satellites, the solar outage can typically cause disruption to the received signal for a few minutes each day for a few days. It will last longer the smaller the antenna involved. A 40cm dish will have a longer period of interference than a 120cm dish. This is because a small dish has a greater signal acceptance angle than a big dish.

How do they affect watching TV?
The effects of a sun outage range from partial degradation (increase in the error rate) to total destruction of the signal. During this time interference may occur with picture quality and sound when watching television. Sun outages do not affect internet or phone service. 

Sun Outage Prediction Parameter
Time, date and duration of sun outage problem depends on some parameters.
  • Latitude of the receiving antenna
  • Latitude of the satellite
  • The diameter of the receiving antenna
  • The beam width of the receiving antenna
  • The apparent radius of the sun as seen from the Earth (about 0.25°)
  • 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
Outage Angle
Those parameter 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 sun at the time when sun outage or signal degradation begins or ends.

Figure: sun outage angle.

Frequency = Down link Frequency in GHz.
Diameter = Dish diameter of ground station receive antenna in meters.


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