User's Manual

10 MDS TransNET I/O Guide MDS 05-2708A01, Rev. A
4.3 A Word About Radio Interference
The MDS TransNET 900™ transceivers share frequency spectrums with other
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. However, the radio’s 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/protocol techniques.
In general, keep the following points in mind when setting up your
communications 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. If possible, use a directional antenna at remote sites. 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. (The use of a
directional antenna may not be possible in a simplex peer-to-peer network,
where all remotes are designed to communicate with one another.)
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 vertical polarization in this
band, an additional 20 dB of attenuation to interference can be achieved by
using horizontal polarization.
4. Multiple MDS TransNET 900™ systems can co-exist in proximity to each
other with only very minor interference as long as they are each assigned a
unique network address. Each network address has a different hop pattern.
5. If constant interference is present in a particular frequency zone, it may be
necessary to “lock out” that zone from the radio’s hopping pattern. The radio
includes built-in software to help users remove blocked frequency zones
from its hopping pattern. Refer to the discussion of the
SKIP ( Page 33 )
command for more information.
6. If interference problems persist even after removing blocked zones, try
reducing the length of data streams. Groups of short data streams have a
better chance of getting through in the presence of interference than do long
streams.
7. The power output of all radios in a system should be set for the lowest level
necessary for reliable communications. This lessens the chance of causing
unnecessary interference to nearby systems.
4.4 Antenna & Feedline Selection
Antennas
The equipment can be used with a number of antennas. The exact style used
depends on the physical size and layout of a system. Contact your MDS
representative for specific recommendations on antenna types and hardware
sources.
In general, an omnidirectional antenna (Figure 9 and Figure 10) is used at the
master station site in an MAS system. This provides equal coverage to all of
the remote sites.