NorthStar 961 Install Manual page 50

SECTION TWO - Installation
Table 3: Troubleshooting the GPS/DGPS antenna installation (continued)
Symptom
High beacon SNR or low signal.
When vessel interference is still
present:
When the source of the
interference is found:
Poor, intermittent, or no beacon signal when
using a known-good loop or combo
antenna.
a. The GPS receiver AA180 supplies the 5.5 VDC to the AN150 active GPS antenna.
b. Testing the GPS portion of the splitter and a combo antenna: When using a combo antenna and
splitter, the splitter gets 7.75 VDC from the beacon receiver, and then feeds the combo pre-amp with
that same voltage level. The splitter must have this 7.75 VDC supplied to the differential port for the
GPS and the differential signal to be passed through the splitter. To test the GPS portion of the
combo antenna, disconnect the splitter and plug the combo antenna directly into the GPS BNC
connector (provided that the 5.5 VDC is present). This troubleshooting technique effectively
eliminates the splitter from the equation. If the splitter is bad, GPS may not work when connected
normally (provided that the 7.75 VDC from the beacon receiver is present). Note that under normal
circumstances the combo antenna should never be plugged directly into the GPS port because the
voltage feeding the amplifier is too low and will result in low GPS signal levels being sent to the GPS
receiver.
c. The beacon receiver (8500) supplies the 7.75 VDC to the 8410 (in the case of a whip-type antenna
installation), or the splitter (in the case of a combo antenna installation), which in turn feeds the
combo antenna.
Page 40
Possible Solutions/Reasons
•
Turn off all electrical devices and equipment on the vessel,
then check for improvement. Check fluorescent lights,
gauges, and so forth. Be creative! Check for power-line
interference by moving away from the dock and/or the
marina. Verify that the antenna is mounted in accordance with
the recommendations shown in Figure 5.
•
Isolate to the interfering device, with breaker panel if
necessary.
•
Experiment with different grounding locations (the best
ground is the ocean). Drop a temporary wire attached to the
8410 black wire over the side of the vessel to see if the
interference source can be fixed by grounding techniques.
• Disconnect shore power and move away from the dock and/
or marina (power lines and lights can cause interference).
•
Temporarily relocate the 8410 or combo antenna as far away
as possible from the interfering source, and monitor the effect
on reception. If it improves, consider relocating the antenna or
try to determine if the interference can be eliminated at its
source.
•
Normally, noise that affects an 8410 DGPS coupler won't
affect a combo antenna, and vice versa. Consider temporarily
changing antenna types to determine the effects on signal
reception.
•
Check the proximity of the antenna to radar antennas or other
transmitting devices, such as INMARSAT. A radome can
affect H-field antennas even when power is off. Hint: To test
for the best location, move the antenna and coax to
temporary locations using an over-the-deck length of coax,
then relocate as necessary.
961/962 INSTALLATION MANUAL Revision A