SXBlue GPS Reference Manual
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Type 1 and Type 9 messages, both of which contain similar information. These two messages
contain pseudorange corrections and range rate corrections to each GPS satellite.
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The Type 2 message contains delta differential corrections that are used when the remote
receiver is using a different satellite navigation message than used by the base station.
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The Type 5 message contains GPS constellation health information used for improving tracking
performance of a GPS receiver
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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.
Note - RTCM is a local area data standard. This means that when positioning with
external correction input to the SXBlue GPS from an external source or outputting
corrections from the SXBlue GPS to another GPS receiver, performance will degrade
as a function of distance from the base station. The additional degradation will
depend on the difference in observed orbit and ionospheric errors between the
reference station and the remote unit. A general rule of thumb would be an additional
1 m error per 100 miles. This error is often seen as a bias in positioning, resulting in
a position offset. The scatter of the receiver is likely to remain close to constant.
The RTCM SC-104 data output by the SXBlue GPS is converted from the RTCA SC-159
data broadcast by SBAS networks.
Appendix D - Resources contains the contact information should you wish to purchase a
copy of the RTCM SC-104 specification.
4.3 Configuring SXBlue GPS
All aspects of SXBlue GPS operation may be configured through the serial port with the use
of NMEA 0183 commands via a terminal software, or using the PocketMAX utility discussed
in the PocketMAX manual. These commands are described in the Chapters 8 and 9. The
following items are user-configurable:
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Selecting one of the two on-board applications (SBAS or e-Dif, if present)
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Setting the baud rate of the serial RS-232 port
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Choosing which NMEA data messages to output on the dual serial ports and the update rate of
each message
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Setting the maximum differential age cut-off
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Setting the satellite elevation angle cut-off mask
4.4 Firmware
The software that runs the SXBlue GPS is often referred to as firmware since it operates at
a low level. There are two types of firmware within the SXBlue GPS for the on-board digital
signal processor (DSP) and the ARM processor. Each of these types of firmware may be
upgraded in the field through the main serial port as new revisions become available.
The ARM processor of the SXBlue GPS engine supports two simultaneous versions of
firmware. Only one of them is in operation at any given time. These two versions of
firmware may have different functionality, and are also referred to as applications.
