__________________________________________________________ Radio Wave Propagation
Fading is caused by variations in signal strength, such as absorption of the
RF energy by the ionosphere.
Multipath fading occurs when a transmitted signal divides and takes more
than one path to a receiver and some of the signals arrive out of phase,
resulting in a weak or fading signal.
Figure 2-Sum 10. Multipath Transmission
Some transmission losses that affect radio-wave propagation are ionospheric
absorption, ground reflection, and free-space losses.
Electromagnetic interference (EMI), both natural and man-made, interferes
with radio communications.
The maximum usable frequency (MUF) is the highest frequency that can be
used for communications between two locations at a given angle of incidence
and time of day.
The lowest usable frequency (LUF) is the lowest frequency that can be used
for communications between two locations.
Figure 2-Sum 11. Refraction of Frequency below the Lowest Usable Frequency (LUF)
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