Delorme PN-20 User Manual download pdf (Page 8)

travel from the satellite to the receiver. Since radio waves travel at the speed of light, the time dif-

ference can be used to calculate the distance from the satellite to the GPS receiver.

The satellite’s identity code provides the location of the satellite, and the distance to the receiver

creates a sphere of possible locations for the GPS receiver. Without more information, the receiver

knows only that it is located somewhere on that sphere.

Two additional satellites are necessary to narrow down the receiver’s position. Each of these

satellites sends a similar radio message containing time and identity information. The GPS receiver

checks the orbital location of each satellite and uses the elapsed time to create two additional

spheres of possible locations. These three spheres intersect at two points; however, one of these

points is eliminated because it is far away from the Earth’s surface. Therefore, the second point

is assumed to be correct. The data from these three satellites provides the receiver with a two-

dimensional location.

Data acquired from a fourth satellite pinpoints the receiver’s exact location. This additional position-

ing information allows the GPS receiver to calculate its elevation, which is particularly important for

GPS users in mountainous locations.

GPS Position Accuracy

Any buildings, natural structures, or heavy foliage that obstruct the GPS antenna’s view of the sky

prevent satellite signals from reaching the receiver and decrease the accuracy of your position.

Frequently Asked Questions

Can I install non-DeLorme maps on the Earthmate GPS PN-20?

DeLorme’s professional GIS software, XMap

, allows you to register non-DeLorme maps and

transfer them to the Earthmate GPS PN-20.

How can I improve the life of my batteries?

When the backlight is on, it consumes a large part of the battery. Changing the backlight timer to

turn off after 15 seconds could double the life of your batteries. For information on changing the

backlight timer, see ToModifytheBacklightTimer on page 69.

Getting Started

Note:PlacingtheEarthmate

GPSPN-20inabackpack

pocketorjacketshouldnot

resultinproblemswithGPS

positionaccuracy.

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 92 93

No comments

Delorme PN-20 User Manual Page 8