Topband: Fading

[Kris Mraz]

I know that fading can be caused by phase rotation of the arriving signal.
Can fading be caused by the signal changing arrival angle over time
(1-3 seconds)?
I ask this because of something I observed while attempting to tune my
Shared Apex Loop (SAL)
antenna the other night.

In the forward direction I tuned in a strong, distant AM broadcast
signal that was fairly steady
strength-wise. It would vary less than an S unit as seen on my radio
S-meter (FTdx5000). Then I
switched to the reverse direction. From the SAL backside the signal
experienced rapid fading
from S0 to S8.

Looking at the elevation pattern of the SAL (or just about any RX
antenna design) it can be seen
that the forward direction has a broad gain pattern around the 20
degree arrival angle. In the reverse
direction there is a deep steep null near that reverse angle. From
this I assumed that the signal was
changing arrival angle, moving into and out of that deep null. Is this
the correct analysis?


Kris N5KM