Viavi 87339, Руководство по эксплуатации

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Testing
4 -8
4.1.5 GPS Receiver Communication
Some receivers may have maintenance pages the user can access to view SV parameters
and positional information. Access may either be directly via a display/control or by the
use of proprietary software.
For a standardized means of accessing all receiver data most receivers support the
NMEA-183 protocol. NMEA -183 compliant receivers send data continuously through
either a serial or USB interface, in the form of text sentences, which may be monitored by
PC using a suitable application. The NMEA-183 protocol supports six basic sentences,
and each provides a different data type. Refer to table 4-1. The first word in each
sentence is the three letter data type.
Table 4-1 Basic NMEA-183 Sentences
The information from the GSA sentence can be used to verify if the receiver has achieved
a position fix and may be used in TTFF measurements. The GSV sentence provides the
C/N0 (carrier-to-noise) ratios for each satellite that the receiver is tracking, which may be
used for sensitivity tests.
Data Type Description
GGA Fix information
GLL Latitude and longitude information
GSA Overall satellite data
GSV Detailed data for satellites in view
RMC Recommended minimum data for GPS
VTG Vector track and speed over ground