SXBlue II GPS Series Technical Reference Manual
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Install the antenna in the best location for the application, such as the center line of the
vehicle or vessel. The position calculated by the beacon receiver is measured to the
center of the antenna.
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Do not locate the antenna in areas that exceed environmental conditions that are
specified.
2.4 OmniSTAR Services
OmniSTAR is a worldwide terrestrial DGPS service that provides correction data to subscribers
of the system with the use of a geostationary transponder.
2.4.1 System Overview
OmniSTAR is a wide area DGPS service. The information broadcast by this service is based
upon a network of reference stations placed at geographically strategic locations. The network
stations communicate GPS correction data to control centers where it is decoded, checked, and
repackaged into a proprietary format for transmission to a geostationary L-band
communications satellite. The satellite rebroadcasts the correction information back to earth
over a large signal footprint where the SXBlue II-L GPS, L-band differential satellite receiver,
demodulates the data.
The OmniSTAR signal content is not RTCM SC-104, but a proprietary wide-area signal that is
geographically independent. With this service, the positioning accuracy does not degrade as a
function of distance to a base station, as the data content is not composed of a single base
station’s information, but an entire network’s information. When the SXBlue II-L GPS integrated
L-Band receiver demodulates the proprietary signal, it converts it into a local-area format for
input to the internal GPS receiver (standard RTCM SC-104, message Type 1).
The SXBlue II-L GPS receiver interpolates corrections from the wide-area signal, specific to the
location using Virtual Base Station (VBS) processing algorithms. The resulting RTCM
corrections are those that would be calculated if a reference station were set up at the present
location. This type of solution ensures a consistent level of accuracy across the entire coverage
area.
2.4.2 Signal Reception
The OmniSTAR L-band signal is a line-of-sight UHF signal that is similar to GPS. There must be
a line of sight between the SXBlue II-L GPS’s antenna and the geostationary communications
satellite in order for the L-band differential receiver inside the SXBlue II-L GPS to acquire the
signal.
Various L-band communications satellites are used for transmitting the correction data to
OmniSTAR users around the world. When the SXBlue II-L GPS has acquired an OmniSTAR
signal, the elevation and azimuth are available in the menu system in order to troubleshoot line
of sight problems. Contact OmniSTAR for further information on this service and actual
worldwide signal broadcast coverage maps. OmniSTAR contact information is provided in
Appendix D of this manual.
