GE MDS iNET Series, Справочное руководство

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05-2806A01, Rev. L MDS iNET Series Reference Manual 109
These requirements can be quickly determined in most cases. A possible exception is the last item—veri-
fying that an unobstructed transmission path exists. Radio signals travel primarily by line-of-sight, and
obstructions between the sending and receiving stations will affect system performance. If you are not
familiar with the effects of terrain and other obstructions on radio transmission, the discussion below will
provide helpful background.
4.1.3 Equipment Grounding—Important
To minimize the chance of damage to the transceiver and connected equipment, a safety ground (NEC Class
2 compliant) is recommended which bonds the antenna system, transceiver, power supply, and connected
data equipment to a
single-point ground, keeping all ground leads as short as possible.
Normally, the transceiver is adequately grounded if the supplied flat mounting brackets are used to mount
the radio to a well-grounded metal surface. If the transceiver is not mounted to a grounded surface, it is rec-
ommended that a safety ground wire be attached to one of the mounting brackets or a screw on the trans-
ceiver’s case.
The use of a lightning protector is recommended where the antenna cable enters the building. Bond the pro-
tector to the tower ground, if possible.
4.1.4 Terrain and Signal Strength
While the license-free 900 MHz band offers many advantages for data transmission services, signal propa-
gation 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 remote 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
(–80 dBm for iNET-II) or stronger will provide acceptable performance in many systems. While the equip-
ment will work at lower-strength signals, signals stronger than – 77 dBm provide a “fade margin” of 15 dB
to account for variations in signal strength that may occur from time-to-time. RSSI can be measured with a
terminal connected to the
COM1
Port or with a HTTP browser to the
LAN
(Ethernet) connector. (See
“Antenna Aiming” on Page 115 for details.)
4.1.5 Antenna & Feedline Selection
NOTE:
The transceiver is a Professional Installation radio system and must be installed by trained profes-
sional installers, or factory trained technicians.
This text that follows is designed to aid the professional installer in the proper methods of main-
taining compliance with FCC Part 15 limits and the +36 dBm or 4 watts peak E.I.R.P limit.
Antennas
The equipment can be used with a number of antennas. The exact style used depends on the physical size
and layout of a system. Contact your factory representative for specific recommendations on antenna types
and hardware sources.
In general, an omnidirectional antenna (Figure 4-5) is used at the Access Point station site. This provides
equal coverage to all of the Remote Gateway sites.