Satellite Sun Interference

How does the sun cause interference to my satellite reception?

Geostationary satellites are stationed at approximately 22,300 miles (36,000 kilometers) from Earth and located directly over the equator. Given the equator is offset by 22.5 degrees, the sun aligns directly with satellites and receiving earth stations twice a year—once in the spring and once in the autumn (Figure 1). This event is called a sun outage, and is also known as sun fade or sun transit.

The heat emitted by the sun is an intense source of noise radiated at all frequencies, including the frequency range communication satellites use. That noise is called thermal noise. When the sun—and its thermal noise—aligns perfectly with a satellite and the receive antenna on the ground (line-of-sight), the the noise floor, as seen by the receive earth station, is significant enough that it rises above the satellite's carrier signal and causes a temporary loss of reception (Figure 2).

A sun outage occurs because the earth station cannot distinguish between the energy from the sun and its intended communication signal. This is similar to when one is listening to a person talk immediately adjacent to them and a loud noise suddenly drowns out the voice of the person speaking, such that all that can be heard is that loud noise, until the noise either stops or moves far enough away to again hear the speaking person's voice.

Figure 1/Figure 2: The sun's thermal noise overpowers the signal coming from the satellite.

The duration of the solar interference depends on the receive antenna's location on the Earth, the satellite's orbital location above the equator, the size of the receive antenna and the reception frequency. These sun outages start with a signal loss of only a few minutes. The outages start small—when the sun is very near alignment with the satellite and the earth station.

The sun's thermal energy is strong enough to temporarily interfere with the satellite signal and cause an outage as it approaches direct alignment. Each day as the sun moves further north, the sun's alignment with the satellite and earth station move ever so slightly. As the sun becomes more aligned with the satellite and the earth station on the ground, the outage duration increases. Peak outage time occurs when the sun, satellite and the earth station are exactly aligned with each other. The interference declines gradually as the sun starts moving away from the satellite and earth station alignment, until it is no longer a factor—until the next interference season when the sun starts heading south (northern hemispheric in autumn).

Given that all geostationary satellites are over the same geographic plane—the equator—and orbiting at the same distance, 22,300 miles or 36,000 kilometers, the sun outage will apply to every antenna at a given location. For instance, if there are four antennas looking at four different satellites (assuming the dishes are of the same size and same frequency reception), the solar outage will travel through all four satellites and antennas at that location in the same day. The four events will happen at different times of day for each satellite, as Earth's rotation creates alignment.

The duration of the outage is inversely related to the size and frequency of the satellite receive dish. The larger the antenna, the shorter the duration and intensity of the outage. Similarly, the smaller the dish, the great the duration and intensity.

For example, a 3.8 meter C-band receive antenna located in Toronto, Ontario, Canada, receiving from Intelsat's Galaxy 16 satellite will have the following outages for the spring of 2010.

Spring Interference

Date	Time (UTC)	Duration
1 March 2010	18:55	5 minutes
2 March 2010	18:53	7 minutes
3 March 2010	18:53	8 minutes
4 March 2010	18:53	7 minutes
5 March 2010	18:54	4 minutes

Using the same example, when the dish size increases to 9 meters, the outage time decreases in both minutes and number of days.

Spring Interference

Date	Time (UTC)	Duration
2 March 2010	18:55	4 minutes
3 March 2010	18:55	4 minutes
4 March 2010	18:55	3 minutes

Using the same 3.8 meter dish and C-band frequency noted above, the sun interference in Los Angeles is noted in the below chart. The interference starts four days later than in Toronto due to Los Angeles being lower in latitude than Toronto, but has very similar outage durations.

Spring Interference

Date	Time (UTC)	Duration
4 March 2010	18:34	5 minutes
5 March 2010	18:33	7 minutes
6 March 2010	18:32	8 minutes
7 March 2010	18:32	7 minutes
8 March 2010	18:33	4 minutes

One of the many valuable tools on MyIntelsat, the company's customer extranet, includes an easy-to-use sun interference calculator. To gain access to MyIntelsat, Intelsat customers should connect with their Intelsat Sales Director or simply send an email request to myintelsat@intelsat.com.