User's Manual

MDS 05-2708A01, Rev. D MDS TransNET I&O Guide 9
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 tools to help users remove blocked frequency
zones. Refer to the discussion of the SKIP command (Page 41) for more
information. In the USA, a maximum of four zones may be skipped, per
FCC rules. Check the regulatory requirements for your region.
6. Interference can also come from out-of-band RF sources such as paging
systems. Installation of a bandpass filter in the antenna system may bring
relief. (Contact the MDS Customer Service Department for
recommendations and sources of suitable filters.)
7. Proper use of the RETRY and REPEAT commands may be helpful in areas
with heavy interference.
The RETRY command sets the maximum number of times (0 to 10) that a
radio will re-transmit upstream data over the air. Values greater than 0
successively improve the chances of a message getting through when
interference is a problem.
The REPEAT command sets a fixed number of unconditional
retransmissions for downstream data.
8. The RF 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.
3.4 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 repre-
sentative for specific recommendations on antenna types and hardware
sources.
In general, an omnidirectional antenna (Figure 7 and Figure 8) is used at the
Master station site in an MAS system. This provides equal coverage to all of
the Remote sites.
NOTE: Antenna polarization is important. If the wrong polarization is used, a signal re-
duction of 20 dB or more will result. Most systems using a gain-type omnidirec-
tional antenna at the Master station employ vertical polarization of the signal;
therefore, the Remote antenna(s) must also be vertically polarized (elements
oriented perpendicular to the horizon).
When required, horizontally polarized omnidirectional antennas are also avail-
able. Contact your MDS representative for details.