Hemisphere GPS Crescent V100 Series, User Manual

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2: Crescent V100 Operation
Automatic SBAS (WAAS, EGNOS, MSAS and others) Tracking
The Crescent V100 will automatically scan and track SBAS signals
without the need to tune the receiver. The Crescent V100 features
two-channel tracking that provides an enhanced ability to maintain
a lock on a SBAS satellite when more than one satellite is in view.
This redundant tracking approach results in more consistent
tracking of a SBAS signal when in an area where signal blockage of
a satellite is possible.
Beacon Operation
Many marine authorities, such as coast guards, have installed
networks of radiobeacons that broadcast DGPS corrections to users
of this system. With the increasing utility of these networks for
terrestrial applications, there is an increasing trend towards
densification of these networks inland. The dual channel beacon
receiver in the V110 is able to operate in manual or automatic
tuning mode, or using database mode will select the closest station
in compliance with IEC 61108-4 standards.
e-Dif
Extended differential (e-Dif) is an optional mode in which the
receiver can perform with differential-like accuracy for extended
periods without the expense or uncertainty of an external
differential service. It models the effects of ionosphere,
troposphere, and timing errors for extended periods by computing
its own set of pseudo-corrections. e-Dif may be used anywhere
geographically and is especially useful where SBAS networks have
not yet been installed, such as South America, Africa, Australia and
Asia.
The positioning performance of the receiver unit is dependent upon
the rate at which the environmental modeling of e-Dif and the
environmental errors diverge. The more that e-Dif is able to model
the errors correctly, the longer that e-Dif will provide reliable,
accurate positioning. The accuracy of positioning will have a slow
drift that limits use of e-Dif to approximately 30 to 40 minutes,