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Loran TD System
LORAN C is a radio navigation aid operated and maintained in the United
States by the United States Coast Guard. The name LORAN is an acronym for
“LOng RAnge Navigation”. The LORAN system covers the entire United States
and the U.S. Coastal Confl uence Zone. From the perspective of a mariner, the
system is used for ocean and coastal navigation. It can be used as a supplemental
system for harbor and harbor approach navigation, and it is used for inland
navigation by recreational vehicles.
LORAN TD Feature
The LORAN TD (Time Delay) feature eases the transition from using LORAN
to using GPS. The GPSMAP unit automatically converts GPS coordinates to
LORAN TDs for those who have a collection of LORAN fi xes for favorite fi shing
spots and other waypoints recorded as TDs. You can display your position as a TD
or enter waypoints as TDs. The accuracy to be expected from this conversion is
approximately thirty meters. When the unit is placed in the LORAN TD format
mode, it simulates the operation of a LORAN receiver. Position coordinates may
be displayed as TDs, and all navigation functions may be used as if the unit was
actually receiving LORAN signals.
Using the LORAN TD Format
When creating new waypoints using LORAN TD coordinates, you must set
the correct LORAN chain number and secondary stations in the Setup TD fi eld
before storing the waypoint. After the waypoint is stored in unit memory, it will
always reference the LORAN chain number and secondary stations currently
selected in the Setup TD fi eld. If you enter a different LORAN chain number,
change the secondary stations or offsets in the Setup TD fi eld, the active waypoint
information will refl ect those changes. Since the GPSMAP 76S does not rely on
the LORAN signal for navigation, it can reference a different GRI chain and/or
secondary stations and still navigate to the location stored in memory.
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Appendix G
Loran TD
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