SIMREX MAN.ESS-01, Rev. F
DataMover ESS User’s Guide
145
SIMREX Corporation
found in the
CHAPTER-3 EMBEDDED MANAGEMENT SYSTEM
sec-
tion Page 27
.
5.1.7 A Word About Radio Interference
The transceiver shares the radio-frequency spectrum with other 900
MHz services and other Part 15 (unlicensed) devices in the USA. As
such, near 100% error-free communications may not be achieved in a
given location, and some level of interference should be expected. How-
ever, the radio’s flexible design and hopping techniques should allow
adequate performance as long as care is taken in choosing station loca-
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.
• Systems installed in rural areas are least likely to encounter interfer-
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 confine 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 filter 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 13
.) 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 57 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
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