User's Manual

MDS 05-6302A01, Rev. B MDS Mercury 16E Technical Manual 55
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 problems persist, 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.
• The power output of all radios in a system should be set for the low-
est level necessary for reliable communications. This lessens the
chance of causing unnecessary interference to nearby systems.
If you are not familiar with these interference-control techniques, con-
tact your factory representative for more information.
6.9 Radio (RF) Measurements
There are several measurements that should be performed during the ini-
tial installation. These will confirm proper operation of the unit and if
recorded, can serve as a benchmark for troubleshooting should difficul-
ties appear in the future. These measurements are:
• Transmitter Power Output
• Antenna System SWR (Standing Wave Ratio)
• Antenna Heading Optimization (RSSI)
These procedures may interrupt traffic through an established network
and should only be performed by a skilled radio-technician in coopera-
tion with the network manager.
Transmitter Power Output and Antenna System SWR
Introduction A proper impedance match between the transceiver and the antenna
system is important. It ensures the maximum signal transfer between the
radio and antenna. The impedance match can be checked indirectly by
measuring the SWR (Standing Wave Ratio) of the antenna system. If the
results are normal, record them for comparison for use during future
routine preventative maintenance. Abnormal readings indicate a pos-
sible trouble with the antenna or the transmission line that will need to
be corrected.
The SWR of the antenna system should be checked before the radio is
put into regular service. For accurate readings, a wattmeter suited to the
frequency of operation is required. One example of such a unit is the
Bird Model 43
™
directional wattmeter with an appropriate element
installed.
The reflected power should be less than 10% of the forward power
(2:1 SWR). Higher readings usually indicate problems with the
antenna, feedline or coaxial connectors. If the reflected power is more
than 10%, check these areas for damage.