Cambium Networks PTP 250, User Manual

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PTP 250 User Guide Link planning
phn-2510_002v000 (Mar 2012) 2-11
Path loss considerations
Path loss is the amount of attenuation the radio signal undergoes between the two ends of
the link.
Calculating path loss
The path loss is the sum of the attenuation of the path if there were no obstacles in the
way (Free Space Path Loss), the attenuation caused by obstacles (Excess Path Loss) and a
margin to allow for possible fading of the radio signal (Fade Margin). The following
calculation needs to be performed to judge whether a particular link can be installed:
capability seasonal fade excess space free
L L L L L
_
Where
is
space free
L
_
Free Space Path Loss (dB)
excess
L
Excess Path Loss (dB)
fade
L
Fade Margin Required (dB)
seasonal
L Seasonal Fading (dB)
capability
L
Equipment Capability (dB)
Adaptive modulation
Adaptive modulation ensures that the highest throughput that can be achieved
instantaneously will be obtained, taking account of propagation and interference. When
the link has been installed, web pages provide information about the link loss currently
measured by the equipment, both instantaneously and averaged. The averaged value will
require maximum seasonal fading to be added, and then the radio reliability of the link can
be computed.