MDS 05-4055A01, Rev. A
MDS entraNET 900 System Guide (Preliminary)
105
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Figure 5-3. Mounting Brackets Dimensions
5.1.2 Site Selection
Suitable sites should provide:
• Protection from direct weather exposure
• A source of adequate and stable primary power
• Suitable entrances for antenna, interface or other required
cabling
• Antenna location that provides as unobstructed a transmission
path as possible in the direction of the associated station
(
s
)
These requirements can be quickly determined in most cases. A possible
exception is the last item—verifying that an unobstructed transmission
path exists. Radio signals travel primarily by line-of-sight, and obstruc-
tions between the sending and receiving stations will affect system per-
formance. If you are not familiar with the effects of terrain and other
obstructions on radio transmission, the discussion below will provide
helpful background.
5.1.3 Terrain and Signal Strength
While the license-free 900 MHz band offers many advantages for data
transmission services, signal propagation is affected by attenuation from
obstructions such as terrain, foliage or buildings in the transmission
path.
A line-of-sight transmission path between the central transceiver and its
associated transceiver site
(
s
)
is highly desirable and provides the most
reliable communications link.
Much depends on the minimum signal strength that can be tolerated in
a given system. Although the exact figure will differ from one system to
another, a Received Signal Strength Indication (RSSI) of –77 dBm or
stronger will provide acceptable performance in many systems. While
the equipment will work at lower-strength signals, signals stronger than
– 77 dBm provide a “fade margin” of 15 dB to account for variations in
2.75
˝ (7 cm)
7.25˝ (18.4 cm)
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