NorthStar 951X, Руководство по установке, Страница: 27 / 80

SECTION TWO - Installing the unit
951/952 INSTALLATION MANUAL Revision B Page 17
high as possible: Values of 15 and higher are preferable, and anything
below 10 could indicate poor reception.
Installing the
AN150 antenna
Whereas a loran or differential antenna should be mounted high on the
vessel for best performance, the GPS antenna should be mounted as low
as possible and out in the open to avoid “shading” (placement of the
antenna where it’s partially obscured, by another object, from the signals
it must receive). If you’re mounting the GPS antenna on top of a tower or
mast, understand that the unit will be affected by the pitch and roll of the
vessel. Often, the bow or stern can provide a location where shading is
minimized while serving to keep the antenna low. Be sure that any direc-
tional L-band transmitting antennas (such as radar or satellite communi-
cation antennas) can never point at the GPS antenna, since its internal
preamplifier is quickly destroyed by such radiation.
Figure 7: GPS-only antenna (AN150)
NOTE:
Concerns for the AN205-P that aren’t explained in Table 3,
“Troubleshooting the GPS/DGPS antenna installation,” on
page 35, include the fact that mounting a loop-type antenna in
close proximity to a radome (radar-set antenna) can degrade
signals or cause a complete loss of the beacon signal. The
klystron or magnetron contained in the radar antenna pro-
duces a very dense magnetic 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-stabi-
lized TV or INMARSAT communications dish platforms. Sig-
nal-degradation checks should be performed before finalizing
the installation.
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