Amateur ExtraE2A11
What type of antenna can be used to minimize the effects of spin modulation and Faraday rotation?
B
Answer
Operating procedures and special operations
Type
A
A linearly polarized antenna
B
A circularly polarized antenna
C
An isotropic antenna
D
A log-periodic dipole array
Answer Notes
As radio signals travel through the Earth's ionosphere to and from a satellite, their polarization naturally rotates, which is a phenomenon known as Faraday rotation. Furthermore, many satellites spin in space to maintain attitude stability, causing their transmitting antennas to rotate continuously.
If you use a strictly linearly polarized antenna (such as a standard dipole) on the ground, the received signal will experience severe fading (spin modulation) every time the satellite's signal polarization misaligns with your antenna.
A circularly polarized antenna solves this by being equally receptive to incoming signals regardless of their instantaneous linear orientation. This eliminates the deep signal fades and provides a much more consistent connection with the spinning satellite.
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