ARRL Technician Practice Exam

What causes spin fading in satellite signals?

1. Atmospheric turbulence

2. Rotation of the satellite and its antennas

3. Signal reflections from the Earth

4. Interference from other satellites

The correct answer is: Rotation of the satellite and its antennas

Spin fading in satellite signals primarily results from the rotation of the satellite and its antennas. As the satellite orbits the Earth, the antennas may be oriented in different directions, which affects how the signals are transmitted and received. This rotation can lead to variations in signal strength as the satellite's orientation changes relative to both the Earth station and the signal path. When the satellite spins, the polarization and signal characteristics can fluctuate. These fluctuations can lead to periods of weaker reception, known as spin fading, as certain angles may cause the signal to be partially obstructed or misaligned. This phenomenon is especially significant for communication satellites in low Earth orbit that experience rapid rotation during their passage over a ground station. While atmospheric conditions, reflections from the Earth, and interference from other satellites can affect signal quality, they do not specifically cause the type of fading attributed to the rotational aspects of the satellite itself. Thus, the rotation of satellites and their antennas is the fundamental mechanism behind spin fading.