User Manual

MDS 05-4055A01, Rev. A MDS entraNET 900 System Guide (Preliminary) 109
tion, configuration of radio parameters and software/protocol tech-
niques.
In general, keep the following points in mind when setting up your com-
munications network.
1. 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.
2. 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 com-
paratively narrow lobe, that minimizes interference to (and from)
stations located outside the pattern.
3. 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 filter to attenuate all signals
outside the 900 MHz band.
4. 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 through Multi-
ple Access Points” on Page 8.) Additional isolation can be achieved
by using separate directional antennas with as much vertical or hori-
zontal separation as is practical.
5. 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 “Skip Zone Options Menu” on
Page 31 for more information.)
6. 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.
7. 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.