NorthStar GM1708 961X Installation Manual page 71

961 INSTALLATION MANUAL Revision A
Setting beacon frequency and baud rate
You can set the receiver to operate automatically or be controlled manu-
ally.
Automatic tuning
Northstar's two-channel differential receiver enters automatic differential
mode as soon as corrections are received, and doesn't require any further
supervision for differential operation, automatically tuning to the appro-
priate differential frequency as you move from one differential coverage
area to another or as weather conditions change. First, it finds the differ-
ential frequency and data transfer (baud) rate, then it receives data fully
automatically. The receiver constantly evaluates available radio beacon
signals for signal quality, and selects only the best station. The receiver is
prepared to switch to another frequency automatically, as you travel, as
conditions require.
The unit maintains automatic operation by using its two independent
receiver channels: Channel 1 tracks the best available differential signal
(the one with the lowest data error rate) and sends the demodulated
DGPS corrections to the 961's GPS receiver. Channel 2 continuously
scans the entire differential frequency band (283.5 to 325 kHz), locating
and measuring received DGPS differential signals, which is then stored as
a DGPS differential directory in its battery-powered memory.
If the signal that's received and monitored by Channel 1 degrades for any
reason, such as bad weather between you and the transmitter, the unit
tries to select a better frequency from the differential directory it has
compiled. This feature enables it to switch to the best differential sig-
nal—before affecting your GPS accuracy.
For normal operation, Northstar recommends that you leave both beacon
frequency and baud rate at the AUTO setting. Generally, you'll use auto-
matic mode for everything except specialized applications.
To choose automatic mode:
1. At the RECEIVER INFORMATION screen, press the CURSOR PAD to
highlight the BEACON FREQ field, then press the EDIT key.
2. Press the CURSOR pad left to highlight the AUTO field, then press
the ACCEPT key (or CANCEL to leave the option unchanged).
Manual tuning
You can override the receiver's selection of automatic differential stations
at any time. Under manual control, you manually set the differential fre-
quency and baud rate to tune in a particular differential transmitter. In
manual mode, the differential receiver outputs DGPS corrections only
from the selected station. Although the need for manual operation is rare,
it is easily accessed at the RECEIVER INFORMATION screen. Here, you
SECTION FOUR - Service/Maintenance
Page 61