V103/113 Vector User Guide Chapter 3 - Operation Page 26 of 35
Operation
GNSS Overview
For your convenience, both the GNSS and SBAS operation of the V103/113 features automatic operational
algorithms. When powered for the first time, the V103/113 performs a ‘cold start’ that involves acquiring the
available GNSS satellites in view and the SBAS differential service.
If SBAS is not available in your area, an external source of RTCM SC-104 differential corrections may be used. If
you use an external source of correction data, it must support an eight- data bit, no parity, one stop bit configuration
(8-N-1).
GNSS Operation
The GNSS receiver is always operating, regardless of the DGNSS mode of operation. The following sections
describe the general operation of the V103/113’s internal GNSS receiver.
Note: Differential source and status have no impact on heading, pitch, or roll. They only have an impact on
positioning and heave.
Automatic Tracking
The V103/113’s internal GNSS receiver automatically searches for GNSS satellites, acquires the signals, and
manages the navigation information required for positioning and tracking.
Receiver Performance
The V103/113 works by finding four or more GPS satellites in the visible sky. It uses information from the satellites
to compute a position within 2.5 m. Since there is some error in the GNSS data calculations, the V103/113 also
tracks a differential correction. The V103/113 uses these corrections to improve its position accuracy to better than
0.6 m.
The two main aspects of GNSS receiver performance are 1) satellite acquisition, and 2) positioning and heading
calculation.
When the V103/113 is properly positioned, the satellites transmit coded information to the antennas on a specific
frequency. This allows the receiver to calculate a range to each satellite from both antennas. GNSS is essentially a
timing system. The ranges are calculated by timing how long it takes for the signal to reach the GNSS antenna.
The GNSS receiver uses a complex algorithm incorporating satellite locations and ranges to each satellite to
calculate the geographic location and heading. Reception of any four or more GNSS signals allows the receiver to
compute three- dimensional coordinates and a valid heading.
Differential Operation
The purpose of differential GNSS (DGNSS) is to remove the effects of selective availability (SA), atmospheric
errors, timing errors, and satellite orbit errors, while enhancing system integrity. Autonomous positioning
capabilities of the V103/113 will result in positioning accuracies of 2.5 m 95% of the time. In order to improve
positioning quality to better than 0.6 m 95%, the V103/113 is able to use differential corrections received through
the internal SBAS demodulator or beacon receiver, or through externally-supplied RTCM corrections.
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