Raymarine GPS navigation User Manual download pdf (Page 62)

program and use your own entered value for the variation by selecting the

MANUAL VARIATIONlsof&ey .

When

the1

MANUAL

VARIATIONI

key is pressed, you must first decide

whether the direction of the variation is East or West. The direction already

selected is displayed at the left side of the screen. Press

thmsoftkey

if the

direction should be changed and then press

thmdkey.

“00”

appears next

to the direction character.

Now type the numeric value of variation and

press[wi

The unit will

now be in magnetic mode, but using a fixed variation value. When

the//[

key is pressed, the entered variation will now be applied to all Course and

Bearing readouts. Press

thejjkey

and you will shift back to the mMain

menu directory.

Press-[

a second time to get back to the last used

display mode.

3.10.4.2 Position Corrections- Loran

The NAV 398 unit has Position corrections that are available for use with

Loran-C navigation and corrections that apply to GPS navigation. If you

happen to be using both senors in your system, the menus that appear on the

screen will be determined by the sensor that is currently selected for use. To

apply corrections to the loran L/L you will need to be sure the unit is in the

loran mode. Conversely, be in GPS mode to do GPS corrections.

The NAV 398 includes automatic correction programing for both the Loran

and the GPS modes and these programs are normally operating when the unit

comes from the factory.

Loran Position Corrections

When the loran sensor measures the loran signal time differences, the TD’s

received are rarely perfect by the time they reach your boat. They usually

contain some errors to signal timing developed as the signals travel across

land due to various distortions of the terrain along the path of the radio waves.

Fortunately, the error values are generally known for most of the loran

coverage areas and a table of corrections (ASF) is built into your loran

sensor.The ASF program helps to correct the loran time differences so the

Lat/Lon readouts will match marine chart coordinates and your GPS more

closely.

The NAV unit only uses

Lat.&on

for waypoint navigation calculations.

When navigating to and from waypoints, the loran performs its bearing and

distance, TTG, XTE calculations by comparing the

Lat/Lon

values. Upon

OPERATION 3-49

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Raymarine GPS navigation User Manual Page 62

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