AvMap EKP IV, Руководство пользователя

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52 User Manual
tion of the Azimuth and Elevation of the satellites used to compute a position fix.
The Elevation is the height of the satellite above the horizon, with 5° (lowest)
near the horizon and 90° (highest) being directly overhead (the EKP-IV does
not normally use satellites with Elevations lower than 10°). Azimuth is the
satellite’s location in relation to true north, measured clockwise as a bearing. A
satellite with an Azimuth of 90° is to the east.
The circle contains a number indicating the number of the satellite and it is
green when it is used for the fix solution (red otherwise). On the left side there
are histograms indicating the S/N ratio (SNR). The bar is green when the sat-
ellite is used for the fix (red otherwise). When a valid fix is received, the EKP-
IV displays the current position coordinates, Date, Time, HDOP, VDOP,GS,
TRK and ALT on the GPS page.
7.2 GPS RECEIVER SPECIFICATIONS
•
Receiver : L1, C/A code, DGPS/WAAS Ready
•
Channels : 12
•
Max Solution Update Rate : 10/sec.
•
Cold Start (avg) : < 45 sec.
•
Warm Start (avg) : < 40 sec.
•
Hot Start (avg) : 8 sec.
7.3 HOW GPS WORKS
Each GPS satellite continuously broadcasts two signals: an SPS (Standard Posi-
tioning Service) signal for worldwide civilian use and a PPS (Precise Position-
ing Service) signal for U.S. and Allied military use. The SPS signal is a spread-
spectrum signal broadcast at 1575.42 MHz. The signal is virtually resistant to
multipath and nighttime interference and is unaffected by weather and electri-
cal noise. All commercial and consumer GPS receivers are SPS receivers.
The SPS signal contains two types of orbit data: almanac and ephemeris. Alma-
nac data contains the health and approximate location of every satellite in the
system. A GPS receiver collects almanac data from any available satellite, then
uses it to locate the satellites that should be visible at the receiver’s location.
Ephemeris data represents the precise orbital parameters of a specific satellite.
Receivers listen to signals from many satellites simultaneously and triangulate
a position fix using the interval between the transmission and reception of
each satellite signal (a receiver tracks more satellites than are actually needed
for a position fix, so that if one satellite becomes unavailable, the receiver knows