8
1: Introduction
• The Type 5 message contains GPS constellation health
information used for improving tracking performance of a GPS
receiver
• The Type 6 message contains null information, and is
broadcast so that a beacon receiver demodulating the data
from the broadcast does not lose lock when the beacon station
has no new data to transmit.
• The Type 7 message contains the radiobeacon almanac
information composed of location, frequency, service range,
and health information of sister stations for the currently tuned
beacon.
• The Type 16 message provides users with a 90 character text
string that may contain information regarding the status of the
system, weather warnings, etc.
Radiobeacon DGPS is often referred to as a local-area service, as the
data broadcast is appropriate for use within the coverage range of the
station, and is calculated by a single, local GPS reference station.
Radiobeacon Coverage
Figure 1-1 on page 9 shows the approximate radiobeacon coverage
throughout the world. In this figure, light shaded regions note current
coverage, with beacon stations symbolized as white circles.
The world beacon networks continue to expand. For current coverage,
consult the Hemisphere GPS web site at www.hemispheregps.com.
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