What causes spin fading of satellite signals?

• A. Atmospheric interference
• B. Rotation of the satellite and its antennas
• C. Changes in receiver sensitivity
• D. Signal reflection from the Earth

Answer: (B)

Spin fading of satellite signals occurs mainly due to the rotation of the satellite and its antennas. As the satellite orbits, its rapid rotation can cause the direction of its antennas to change relative to the earth station. This spinning alters the polarization and the effective gain of the antenna, leading to variations in signal strength that can be perceived as fading.

The influence of the satellite's rotation becomes particularly significant if the satellite's antennas are not perfectly aligned with the incoming signal from the Earth, or if they have directional characteristics that change as the satellite spins. Consequently, the reception quality can fluctuate, causing periods of stronger and weaker signals, which is characterized as spin fading.

This phenomenon is distinct from other issues like atmospheric interference, which involves the effects of the atmosphere on signal propagation but does not relate to the physical movement of the satellite. Changes in receiver sensitivity pertain more to the receiver's performance rather than the nature of the transmission from the satellite itself, and signal reflection from the Earth describes multipath effects that result in delay variations rather than direct changes caused by the satellite's motion.