GE MDS iNET 900, Справочное руководство

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05-2806A01, Rev. J iNET Series Reference Manual 135
ence; those in suburban and urban environments are more likely to
be affected by other devices operating in the license-free frequency
band and by adjacent licensed services.
• Use a directional antenna at remote sites whenever possible.
Although these antennas may be more costly than omnidirectional
types, they con
fi ne the transmission and reception pattern to a com-
paratively narrow lobe, that minimizes interference to (and from)
stations located outside the pattern.
• If interference is suspected from a nearby licensed system (such as a
paging transmitter), it may be helpful to use horizontal polarization
of all antennas in the network. Because most other services use ver-
tical polarization in this band, an additional 20 dB of attenuation to
interference can be achieved by using horizontal polarization.
Another approach is to use a bandpass
fi lter to attenuate all signals
outside the 900 MHz band.
• Multiple Access Point units can co-exist in proximity to each other
with only very minor interference. Each network name has a differ-
ent hop pattern. (See
“ Protected Network Operation using Multiple
Access Points” on Page 14.) Additional isolation can be achieved by
using separate directional antennas with as much vertical or horizon-
tal separation as is practical.
• If constant interference is present in a particular frequency zone
(collection of 8 RF channels), it may be necessary to “skip” that
zone from the radio’s hopping pattern. The radio includes built-in
software to help users identify and remove blocked frequency zones
from its hopping pattern. See Page 56 for more information on Skip
Zones.
• If interference problems persist even after skipping some zones, try
reducing the length of data streams. Groups of short data streams
have a better chance of getting through in the presence of interfer-
ence than do long streams.
• The power output of all radios in a system should be set for the low-
est level necessary for reliable communications. This lessens the
chance of causing unnecessary interference to nearby systems.
If you are not familiar with these interference-control techniques, con-
tact your factory representative for more information.
Calculating System Gain
To determine the maximum allowable power setting of the radio, per-
form the following steps: