NorthStar Navigation GM1708 961XD - Manual (Page 48)

SECTION TWO - Installation
Page 38 961 INSTALLATION MANUAL Revision A
Troubleshooting the GPS/DGPS antenna installation
In the following table (troubleshooting the GPS/DGPS antenna installa-
tion), the Northstar AN150 refers to the 12-dB GPS antenna, the North-
star 8410 coupler with whip antenna refers to the beacon receiver
whip-type (E-field) antenna, and the Northstar AN205-P refers to the
combination (combo) GPS/DGPS loop antenna with splitter. Whenever
possible, the best and most efficient way to troubleshoot is to use a
known-good set of cables, a splitter for combo antennas (when applica-
ble), and working antennas as spares for swapping.
INTERFERENCE Electrical, magnetic, or radio frequency (RF)
energy is interfering with the reliable opera-
tion of the unit as shown by high levels of
noise on the DGPS status screen. • Turn off power to each and all of the
vessel’s other instruments and sys-
tems, one at a time, to isolate the
source of the interference.
• Attempt to eliminate the noise through
earth grounding or RF filtering tech-
niques as appropriate to the type of
noise encountered.
GPS The head and processor power up, but poor
GPS SNR readings are obtained even after
running the unit for several minutes. • Check that you have the proper
length of cable and that all connec-
tions are clean and secure.
• Verify the quality of the antenna loca-
tion (the antenna should have a clear
view of the sky). For the correct
antenna placement, see Figure 5.
• See Table 3, “Troubleshooting the
GPS/DGPS antenna installation,” on
page 39.
Table 2: Troubleshooting the installation (continued)
Problem Area Symptom Possible Solutions/Reasons
NOTE:
Concerns for the AN205-P that aren’t explained in the GPS/
DGPS antenna troubleshooting table below include the fact
that mounting a loop-type antenna in close proximity to a
radome (radar-set antenna) can cause signal degradation or a
complete loss of the beacon signal. The klystron or magnetron
contained in the radar antenna produces a very dense mag-
netic field whether or not the radar set is turned on. These
magnetic field effects are also present during the operation of
the servo motors located on gyro-stabilized TV or IMARSAT
communications dish platforms. Signal degradation checks
should be performed before finalizing the installation.