Therefore, a typical installation with 3 dB clear weather link margin is
usually immune from the adverse effects of scintillation. Since scintillation occurs
during hot weather conditions, its effect is insignificant during weather conditions
such as fog and rain. Therefore, the same link margin that provides immunity from
the effects of these weather conditions can effectively provide immunity from the
effects of scintillation.
The effects of scintillation can be minimized by using systems with large beamwidths
and large receive apertures. Additionally, FSO systems using incoherent light sources
such as LED are more immune to the effects of scintillation than those using coherent
246 Chapter 9
light sources such as laser. Distance also makes a difference in the amount of scintillation
experienced, with shorter links experiencing less scintillation. Finally, good
deployment practices can also minimize the effect of scintillation. For example, beam
propagation over sources of air turbulence such as vents and air conditioners should
be avoided. Similarly, installations that result in the optical beam propagating over the
roof of a building can result in a lot of scintillation during hot sunny days and should
be avoided.
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