GE MDS entraNET 900, Техническое руководство

Страница: 161 / 220

05-4055A01, Rev. E MDS entraNET Technical Manual 151
some level of interference should be expected. However, flexible design
and hopping techniques should allow adequate performance, as long as
care is taken in choosing station location, configuration of radio
parameters, and software or protocol techniques.
In general, keep the following points in mind when setting up your
communications network:
• Systems installed in rural areas are least likely to encounter
interference; 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 confine the transmission and
reception pattern to a comparatively narrow lobe, which
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 can be helpful to use horizontal
polarization of all antennas in the network. Because most other
services use vertical 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 filter to attenuate all
signals outside the desired band.
• Multiple AP radios can co-exist in proximity to each other with
very minor interference. Each network address has a different
hop pattern. You can achieve additional isolation by using
separate directional antennas with as much vertical or horizontal
separation as is practical.
• If constant interference is present in a particular frequency zone,
it might be necessary to “skip” that zone from the hopping
pattern. The radio includes built-in software to help you identify
and remove blocked frequency zones from its hopping pattern.
See “Skip Zones Menu” on Page 53 for more information.
• 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 interference
than do long streams.
• Set the power output of all radios in a system for the lowest level
necessary for reliable communications. This reduces the chance
of causing unnecessary interference to nearby systems.
If you are not familiar with these interference-control techniques,
contact your GE MDS Sales Representative or the GE MDS Technical
Support Department for more information.