MDS 05-2708A01, Rev. B
MDS TransNET 900 I&O Guide
9
3.3 A Word About Radio Interference
The MDS TransNET shares the frequency spectrum 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.
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 tools to help users remove blocked frequency
zones. Refer to the discussion of the
SKIP
command (
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. (Recommended: MDS P/N 20-2822A02)
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 (1 to 10) that a
radio will re-transmit upstream data over the air. Values greater than 1
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.
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