Sun transits occur when the sun crosses the earth's equatorial plane during the spring and fall equinoxes (late February or early March; September or October).
At these times, the sun aligns directly behind the satellites for a few minutes each day. When the sun moves directly behind the satellite to your receive antenna, the satellite signal can be overwhelmed by the enormous amount of thermally generated radio frequency (RF) noise radiated by the sun. This can cause reception interference for a few minutes everyday during this occurrence.
The time of occurrence depends both on the geographic location of the earth station and
the location of the satellite. The sun may degrade the signal for several minutes depending
on the antenna size and available link margin, although it is not unusual for the effect to
The number of outages,outage duration and the time of outage depend on the radio emission activity of the sun, the movement of the earth with respect to the sun, the pointing and location of receive antenna, and characteristics of the communication system. Those characteristics, in turn, include the operating receive radio frequency, the receive antenna gain pattern, the clear sky operating carrier-to-noise ratio (C/N), the clear sky equivalent system noise temperature and the minimum acceptable C/N.
When the sun transits occur, the antenna noise temperature varies depending on the antenna size, the elevation angle, location and environment.
Computer generated predictions revealed that sun transits peak times of all days associated with an equinox for a given receive earth station do not differ from each other by more than a minute, and they do not vary much with respect to the year considered. The variations are less than one minute for at least the next decade. Thus for practical purposes, they can be considered the same and invariant with respect to the year they are considered.
The degradation is about the same for most cities, but it differs for different sizes of antennas.
The sun transit predicts are the average of typical 4-year cycle. The start time may vary by +/- 10 minutes, depending on the antenna size and the available link margin.
The predicts are valid approximations intended only for operational planning purposes.
*Source: Telesat Canada.