A Word About Interference - GE MDS 4790M Installation And Operation Manual

MDS 05-3628A01, Rev. B
• An antenna location that provides an unobstructed path to all the
remote radios in the system
• A source of adequate and stable primary power
• Suitable entrances for antenna, interface or other required cabling.
These requirements can be quickly determined in most cases. A possible
exception is the first item—verifying that an unobstructed transmission path
exists. UHF radio signals travel primarily by line-of-sight, and obstructions
between the sending and receiving stations will affect system performance.
If you are not familiar with the effects of terrain and other obstructions on radio
transmission, the following discussion will provide helpful background.
Terrain and Signal Strength
A line-of-sight path between stations is highly desirable and provides the most
reliable communications link in all cases. A line-of-sight path can often be
achieved by mounting each station antenna on a tower or other elevated structure
that raises it high enough to clear surrounding terrain and other obstructions.
The requirement for a clear transmission path depends on the distance to be
covered by the system. If the system is to cover only a limited distance, say 5
km, then some obstructions in the transmission path may be tolerable. For
longer range systems, any obstruction could compromise the performance of
the system, or block transmission entirely.
The signal strength at the receiver must exceed the receiver sensitivity by an
amount known as the fade margin (defined on page 7) to provide reliable
operation under various conditions.
Section 8.2, RF Propagation Planning, beginning on page 74 includes a
detailed discussion of path planning, and should be reviewed before beginning
an installation. Computer software is also available for this purpose that can
greatly simplify the steps involved in planning a path.
On-the-Air Test
If you've analysed the proposed transmission path and feel that it is acceptable,
an on-the-air test of the equipment and path should be conducted. This not only
verifies the path study results, but allows you to see firsthand the factors
involved at each installation site.
The test can be performed by installing a radio at each end of the proposed link
and checking the RSSI value reported at the radio's front panel display. (See
"Front Panel Indicators" on page 21 for procedures.) If adequate signal strength
cannot be obtained, it may be necessary to mount the station antennas higher,
use higher gain antennas, or select a different site for one or both stations.
To prepare the equipment for an on-the-air test, follow the general installation
and operation procedures given in this guide and become familiar with the
operating instructions given in Section 5.0, START-UP AND OPERATION,
beginning on page 21.

A Word About Interference

Interference is possible in any radio system. However, since the radio is
designed for use in a licensed system, interference is less likely because
geographic location and existing operating frequencies are normally taken into
account when allocating frequencies.
The risk of interference can be further reduced through prudent system design and
configuration. Allow adequate separation between frequencies and radio systems.
Keep the following points in mind when setting up your radio system:
MDS 4790M (MPT 1411) I/O Guide 9