Eagle Electronics UltraNavGPS I

ACCURACY

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 what's known as "C/A Code." It's accuracy is

intentionally worsethan the

military's

'P Code." Inthis

manner, civilian users

worldwide can benefit from excellent position fixes. Meanwhile, the military

keeps the most accurate system away

from

potential enemies. Theoreti-

cally, C/Acodecan

give accurate

position

fixes

upto

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 what's

called "Selective

Availability" or SA. This is

small, random errors intention-

ally

added tothe system

your accuracy will

typically

be 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

belier),

and other factors. The smallest ranges on the

plotter

may not be usable if the SA is high, because the position

will move off the

screen even

while

you're sifting still.

TRANSDUCER CONE ANGLES

The sound waves from the transducer spread out into the water in a

cone shaped beam. This looks much like the beam from a flashlight.

The

angle

between the outside edges

of the cone is the cone

angle.

Eagle offers

a choice of transducers with either an 8 or 20 degree cone

angle. The transducer

supplied with the UltraNavGPS has a 20 degree

cone angle. Typically, wide cone

angle

transducers (20 degrees) are

ideal for operating in shallow to medium water

depths. The 20 degree

cone

angle allows

you

to see more

of the underwater world. In 15 feet

of water the 20

degree

cone

covers an area about six feet across. The

8 degree

transducer covers

only about a two foot circle.

The 20 degree transducer is almost always the best to use in fresh

water,

the 8 degree mostly in salt water. In a deep

water environment,

(300

feet - fresh water, 100 feet - salt water)

the narrow cone angle

more desirable. Since the sound energy is concentrated in a smaller

area, it can penetrate

to much

deeper depths.

Don't let this discourage you, however. GPS

by nature has much faster

updates than other

systems (such as

Loran), and

typically

is much easier to

use. Accuracy, even with SA on is still belier than most other navigation

systems. You've

purchased one of the finest

navigation instruments on the

market today. We hope you'll enjoy it for

many years

to come.

The EAGLE GPS Module

This GPS receiver

(manufactured by Rockwell) currently

is used

in

all Eagle

GPS receivers. It's small, rugged, and fast. The five

channel

design

lets it

acquire and track up to five satellites at one time. It transmits position

information to the UltraNavGPS once every second. By incorporating

Rockwell's GPS receiver technology with Eagle's state-of-the-art design

and manufacturing capabilities, Eagle brings to the consumer the most

advanced line of OPS marine

navigation systems available in the world.

50'

100'

150'

200'

8° at 3 db

42 31

20° at 3 db

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