Eagle Electronics II

ACCURACY DGPS (Differential GPS) BEACON RECEIVER SETUP

You may

have heard tales of

extraordinary accuracy

from GPS receivers.

The DOD requires accuracy of 10 to 15 meters from the satellite system.

However, only the military gets

this precision. The

way

the

military keeps

us and other

unauthorized people from

using

the more

precise system

coding. In other

words, the data

coming from the satellites is encrypted.

Civilian GPS receivers use "C/A Code." It's

accuracy is

intentionallyworse

than the

military's "P Code." In

this

manner, civilian users worldwide can

benefit from excellent position fixes. Meanwhile, the military keeps the

most accurate system away

from potential enemies. Theoretically, C/A

code can give

accurate position fixes up

to 15 meters. This is more than

adequate for most people.

However

(as of this

writing), the military isn't satisfied with C/A's potential

accuracy

in the hands of the world. So, it's degrading it further with

"Selective

Availability" or SA. This is small, random errors intentionally

added to the system so

your accuracy

will

typically

within 100 meters.

Of course, accuracy also depends on the angle of the satellite above the

horizon,

signal-to-noise ratio, the number of satellites tracked at one time

(the

more the

better), and otherfactors. The smallest ranges on

the

plotter

may

not be usable if the SA is

high.

The

present position symbol

can move

off the

screen even while

you're sitting still.

Don't let this discourage you,

however. GPS

by nature has much faster

updates than other

systems (such as Loran), and

typically

much easier

to use.

Accuracy, even with SA on is still better than most

other

navigation

systems. You've

purchased

one of thefinest

navigatiorrinstruments

on the

market

today. We hope you'll enjoy

it for

many years

to come.

The EAGLE EGP-1 GPS Module

This GPS receiver is currently used in all Eagle GPS receivers. It's

small,

rugged, and fast. The five channel design lets it track all satellites in view

and acquire up

to five satellites at one time. It sends

position information

to the AccuNav II once

every second. By incorporating Rockwell's GPS

receiver

technology with Eagle's state-of-the-art design

and manufactur-

ing capabilities, Eagle brings to the consumer the most advanced line of

GPS marine

navigation systems available in the world.

You'll have to tell the AccuNav II which beacon receiver's data to

expect

and set up

the

parameters for that data. To do

this, first press the MENU

key,

then

pressthe keynexttothe

"CHANGE GPS SETTINGS" label. Now

press the key next to the "SELECT NMEA" label. The screen on the

previous page appears. Press the

key

next to the

desired beacon receiver.

The beacon receiver is selected, now you'll need to set it up for the

frequency

and bit rate of the station you'll be using in your

area.

Repeat

the above steps

getthe

NMEA

screen as shown on the

page. Now

press

the

key next to the

"SETUP BEACON" label. The screen

shown below

appears.

The station frequency and bit

rate are shown on the

right side

of the screen. Press the key

adjacent to the "INC FREQ" to

increase the station frequency

orthe "DEC

FREQ"to decrease

it. Do the same

for the bit rate.

When the station

frequency

and

bit rate are adjusted to their

proper settings, press the key

next to the "EXIT" label. The

AccuNav II returns to the last used GPS screen. The letters "DGPS"

appear

next to the "POSITION" on all screens that show your present

position, showing that the beacon receiver is

working.

To viewthe status of the beacon

signal, pressthe

MENU key until the fourth

menu page appears. Now

press

the key adjacent

to the

"DIFFERENTIAL

GPS STATUS" label. If the beacon receiver is receiving data from the

transmitter and is connected properly

to the AccuNav II, a

screen similar

to the one shown at right ap-

pears.

This

page shows the station ID

number, its frequency

and bit

rate, the "health" of the station

(0 = best, 5 = worst), signal

strength (the higher

the num-

ber, the better), and the

signal-

to-noise ratio (SNR). The high-

erthe SNR

number, the better.

pcn

8 37

fl15 OK OK OK OFF

fl13 OK OK OK OFF

tJ02 OK OK OK ON

It27 OK OK OK ON

26 BAD OK BAD OH

ah1

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