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958 Operator’s Manual, Rev. A
repeatable accuracy has served harbormasters and fishermen
so well over the last 25 years.
Loran, however, isn’t as proficient as GPS in
absolute accuracy
,
or when visiting a spot for the first time. Loran transmits at a
relatively low frequency (100 kHz—similar to that of an AM
radio). Your ability to get an accurate position fix is directly
related to the following factors:
•
your distance and line geometry from the loran
transmitters and monitor stations
•
the weather, topography, and ionospheric conditions
between you and the transmitters
In these two areas GPS consistently excels when it comes to
absolute accuracy. GPS provides an absolute
accuracy better
than 100 feet nearly everywhere in the world, under virtually
any conditions. This far surpasses the 600-foot absolute
accuracy that’s achievable from a good loran receiver under
ideal conditions.
If you’re used to your Northstar loran’s repeatable
accuracy
always returning you to within a boat length of a lobster trap
or buoy, you won’t necessarily see this same performance with
uncorrected GPS. Instead, you could be as far as 200 feet from
your expected position. This is especially apparent when
you’re displaying the 958’s
CHART
screen, where you can see
your vessel’s plotted position appear to wander around within
an area up to 200 feet in diameter (see figure below).
Summary of Contents for 958
Page 1: ...NORTHSTAR 958 Integrated Navigation System Operator s Manual P N GM958UM Revision A ...
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Page 8: ...Page iv 958 Operator s Manual Rev A ...
Page 26: ...Page 18 958 Operator s Manual Rev A Chapter 1 Getting Started ...
Page 128: ...Page 120 958 Operator s Manual Rev A Chapter 8 Understanding Waypoint Route Navigation ...
Page 150: ...Page 142 958 Operator s Manual Rev A Chapter 10 Understanding Radar Functions ...
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