Technician: Spin Fading

What causes spin fading when referring to satellite signals? [T8B09]

A. Circular polarized noise interference radiated from the sun
B. Rotation of the satellite and its antennas
C. Doppler shift of the received signal
D. Interfering signals within the satellite uplink band

Well, to start with, I suppose we should define “spin fading.”  Spin fading refers to the (sometimes rapid) change in received signal strength you will encounter when listening to amateur radio satellite signals.

It occurs because the satellite is not “fixed” in position during its orbit.  It’s tumbling end-over-end as it makes its pass.  Therefore, the antenna is always moving.

I suppose you could say we’ve just provided our answer, also.  B. Rotation of the satellite and its antennas.  Interfering signals won’t exhibit “fading” characteristics.  Doppler shift will be observed, but it manifests as a slight change in the signal frequency, depending on if the satellite is moving towards you or away from you.  And answer A. Circular(ly) polarized noise interference radiated from the sun just doesn’t make much sense at all.

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