User's Manual

136 MDS iNET 900 Series User’s Guide MDS 05-2806A01, Rev. E.1
station (shown by a lit LINK LED on the front panel) and measure the
reported RSSI value. (See “Antenna Aiming” on Page 125 for details.)
If adequate signal strength cannot be obtained, it may be necessary to
mount the station antennas higher, use higher gain antennas, select a dif-
ferent site or consider installing a repeater station. To prepare the equip-
ment for an on-the-air test, follow the general installation procedures
given in this guide and become familiar with the operating instructions
found in the CHAPTER-3 EMBEDDED MANAGEMENT SYSTEM sec-
tion Page 25.
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 12.) 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