NorthStar 941X Reference Manual page 83

automatic mode
manual mode
Rev. D
These corrections are used by your 941X to improve its position accuracy
to 10 meters—or better—with 2-5 meters accuracy commonly available.
Differential corrections are invaluable when navigating in narrow or
congested areas (such as ports and waterways), or whenever extreme ac-
curacy is required for locating a precise area (retrieving lobster pots, re-
turning to a diving spot, etc.).
Northstar beacon receivers require no manual operation. They automati-
cally tune to the appropriate beacon frequency as you move from one
beacon coverage area to another, or as weather conditions change. Avail-
able radio beacon signals are constantly evaluated for signal quality by
the receiver, and only the best station is selected. As you travel, the
Northstar beacon receiver is prepared to switch to another frequency
automatically, as conditions require.
The 941X, with a Northstar beacon receiver, enters automatic differential
mode as soon as SC-104 DGPS corrections are received and requires no
further supervision, as far as differential operation is concerned. The
beacon receiver maintains automatic operation by using two independ-
ent receiver channels. Channel 1 tracks the best available beacon signal
(the one with the lowest data error rate) and sends the demodulated
DGPS corrections to the 941X GPS receiver. Channel 2 continuously
scans the entire beacon frequency band (283.5 to 325kHz), locating and
measuring received DGPS beacon signals. The unit then stores this in-
formation as a DGPS beacon "directory" in its battery-powered memory.
If the signal being received and monitored by Channel 1 degrades for any
reason, the unit tries to select a better frequency from its beacon mem-
ory. This allows it to switch to the best beacon signal before your GPS
accuracy can be affected.
Automatic mode can normally be used for all but specialized applica-
tions.
At any time, you can override automatic beacon station selection of the
beacon receiver by issuing tuning commands from the keypad. In man
7 — Other Special Functions 7 — Other Special Functions
7 — Other Special Functions 7 — Other Special Functions
Page 75