A Appendix A
There are a limited number of SBAS satellites available, so they may not be readily accessible in
your area. This setting is configured in the Type field on the DGPS page.
Note – SBAS satellites are geosynchronous and centered over the equator. The further away from the equator
the GPS unit, the less visible SBAS satellites are. The Sky Map in SatViewer will show you the position of these
space vehicles relative to your position.
l In SiRF Bin. Mode / In NMEA Mode: indicates which mode you are running in. Some
applications may require GPS data to be sent to the application in the form of a NMEA
message, where other applications require the GPS data be sent as a SiRF Binary message.
Most mapping and navigation applications can use the NMEA message. This setting is
configured with the NMEA/SiRF Binary radio buttons on the GPS page.
l Elev. Mask: displays the current elevation mask. This is the minimum angle above the horizon
that a satellite must be located before it is used and is represented on the sky plot by a red
circle. This setting is useful when using the GPS in areas where there might be obstructions to
the view of low flying satellites (e.g. around buildings or trees). A typical elevation mask setting
is between 5 and 15 degrees to eliminate those satellites from being used to calculate a
position. The purpose for this setting is to increase the accuracy of the GPS. However, by using
this setting, you are reducing the total number of satellites that can be tracked and used by
your GPS receiver. The idea is to eliminate those satellites that may degrade the accuracy of
your GPS receiver.
This is configured in the Masks section of the GPS page.
l Masks: Displays the current PDOP and HDOP mask values as configured in the Masks section
of the GPS page. If the measured Dilution of Precision (DOP) value exceeds the value set for the
corresponding mask, the resulting calculated position will be ignored. In general, as the value of
the DOP decreases, the accuracy of the GPS position increases. DOP values greater than six
usually indicate the GPS position data is of poor quality (due to poor satellite geometry) and
the resulting positions are less accurate.
Note – DOPs can not be displayed in Binary Mode, however, the DOP masks are still in effect.
Satellite Icons
l Unused: A GPS satellite whose signal is being received, but not being used for position
calculations.
l Used: A GPS satellite that is being used to calculate your current position.
l SBAS: A Satellite Based Augmentation System (SBAS) satellite, which can be used for error
corrections. (See the DGPS tab section for more information.)
Leave SNR trails
Creates a dot on the screen for all previous satellite positions that form a trail on the sky plot over
time as the satellite moves across the sky.
Ranger Series Handheld Computer 61
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