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Chapter 3: Operation
GPS Overview
For your convenience, both the GPS and SBAS (WAAS, MSAS, GAGAN and
EGNOS) operation of the V104n features automatic operational algorithms.
When powered for the first time, the V104n performs a "cold start," which
involves acquiring the available GPS satellites in view and the SBAS
differential service.
GPS Operation
The GPS receiver is always operating, regardless of the DGPS mode of
operation. The following sections describe the general operation of the
V104n's internal GPS receiver.
Note: Differential source and status have no impact on heading, pitch, or
roll. They only have an impact on position and heave.
Automatic Tracking
The V104n's internal GPS receiver automatically searches for GPS satellites,
acquires the signals, and manages the navigation information required for
position and tracking.
Receiver Performance
The V104n works by finding four or more GPS satellites in the visible sky. It
uses information from the satellites to compute a position within 3 m. Since
there is some error in the GPS data calculations, the V104n also tracks a
differential correction. The V104n uses these corrections to improve its
position accuracy to better than 1.0 m.
There are two main aspects of GPS receiver performance:
•
Satellite acquisition
•
Position and heading calculation
When the V104n 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. GPS is essentially a
timing system. The ranges are calculated by timing how long it takes for the
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