User Reference and Installation Guide
3-7
© 2006 Microwave Data Systems Inc. All Rights Reserved.
MDS FOUR.9 Series
05-4561A01, Rev. A
3.6.2
Site Evaluation Process
The following steps must be completed to perform a successful site evaluation. Each step in the
process is detailed in the following subparagraphs:
•
Ensure RF Safety compliance: Ensure that appropriate warning signs are properly placed
and posted at the equipment site or access entry. For a complete list of warnings, refer
the Safety Precautions listed at the beginning of this manual.
•
Ensure Compliance with Laws, Regulations, Codes, and Agreements: Ensure that any
installation performed as a result of the site evaluation is in full compliance with applicable
federal and local laws, regulations, electrical codes, building codes, and fire codes.
•
Establish Radio Line of Sight between radios:
The
most critical step in conducting a
site evaluation is confirming a clear visual and radio Line of Sight (LOS) between a
near radio and a far radio. If LOS does not exist, another location must be used.
Radios used in a link must have a clear view of each other, or visual “line of sight”.
Binoculars may be used evaluate the path from the desired location of the near radio to
the desired location of the far unit.
To confirm Line of Sight:
-
Ensure that no obstructions are close to the transmitting/receiving path. Take into
consideration trees, bridges, construction of new buildings, unexpected aerial traffic,
window washing units, etc.
-
Ensure that each ODU can be mounted in the position required to correctly align it
with its link partner.
The radios must also have a clear radio line of sight. If a hard object, such as a mountain
ridge or building, is too close to the signal path, it can damage the radio signal or reduce
its strength. This happens even though the obstacle does not obscure the direct, visual
line of sight. The Fresnel zone for a radio beam is an elliptical area immediately
surrounding the visual path. It varies in thickness depending on the length of the signal
path and the frequency of the signal. The necessary clearance for the Fresnel zone can
be calculated, and it must be taken into account when designing a wireless links.
As shown in the picture above, when a hard object protrudes into the signal path within
the Fresnel zone, knife-edge diffraction can deflect part of the signal and cause it to reach
the receiving antenna slightly later than the direct signal. Since these deflected signals
are out of phase with the direct signal, they can reduce its power or cancel it out
altogether. If trees or other 'soft' objects protrude into the Fresnel zone, they can
attenuate (reduced the strength of) a passing signal. In short, the fact that you can see a
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