TeeJet RX370p - Manual (Page 14)

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RX370P
ChaPter 2 gPs oVerVIew
For operator convenience, both the GPS and differential correction of the RX370p are pre-configured. The
receiver will work out of the box, and for most applications, little user setup is required. When powered for the first
time, the RX370p will perform a “cold start” which involves acquiring the available GPS satellites in view and the
SBAS differential service.
gPs oPeratIon
The GPS engine is always operating, regardless of the DGPS mode of operation. The following sections describe
the general operation of the RX370p’s internal GPS engine.
Automatic Tracking
The GPS engine within the RX370p automatically searches for GPS satellites, acquires the signals, and manages
the navigation information required for positioning and tracking. This is a hands-free mode of operation.
Receiver Performance
The RX370p works by finding four or more GPS satellites in the visible sky and uses the information those
satellites provide to compute an appropriate position (typically within 7-10 ft (2-3 m).) Since there is some error in
the GPS data calculations, the RX370p also tracks a differential correction. The RX370p uses these corrections to
improve its position to less than 3 ft (1 m).
There are two main aspects of GPS receiver performance:
• Positioning
• Satellite acquisition quality
GPS is essentially a timing system. When the RX370p is properly positioned on the vehicle, the satellites transmit
coded information to the antenna in a specific frequency that allows the receiver to calculate a range to each
satellite. The ranges are calculated by timing how long it takes for the GPS signal to reach the GPS antenna.
The GPS receiver uses a complex algorithm incorporating satellite locations and ranges to each satellite to
calculate the geographic location. Reception of any four or more of these signals allows a GPS receiver to
compute 3-dimensional coordinates.
Differential Operation
The Radio Technical Commission of Marine services (RTCM) has a differential service intended for correction
services. This includes the Space Based Augmentation Systems (SBAS), such as the Wide Area Augmentation
System (WAAS) and the European Geo-stationary Navigation Overlay System (EGNOS). The RX370p is
compatible with each of these differential services in addition to e-Dif.
SBAS
The SBAS enabled RX370p operates automatically anywhere within the coverage areas of WAAS, EGNOS, or
other SBAS programs.