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External Frequency
This feature lets you input an external frequency so that you can synchronize the
receiver clock to a more stable external reference. To enable the external frequency
connect the external clock to the EXT REF connector on the front panel and issue the
command $PASHS,EXF. To check the status of this function, issue the command
$PASHQ,EXF. Frequency selection can be made between 10 KHz and 21 MHz in 10-
KHz increments. To disable the external frequency, issue the command
$PASHS,EXF,OFF.
The external frequency parameters are summarized in Table 4.6
The setting of the external frequency is always saved through the power cycle.
Datums
The receiver normally computes and outputs positions in the WGS-84 coordinate
reference frame. However, it is possible to output positions in NMEA messages in a
number of different pre-defined datums, as well as in a user defined datum.
To set the receiver to output positions in a different datum, use the $PASHS,DTM
command. Once set to a different datum, then all position outputs in NMEA messages
such as GGA and GLL and the position dare referenced to the chosen datum. For a
list of Datums, refer to Appendix B, Reference Datums and Ellipsoids.
If the list of datums does not include a datum of interest to the user, a user defined
datum may be created and supplied to the receiver. This is done using the command
$PASHS,UDD command along with the $PASHS,DTM command. Prior to using
these commands, the user must first define the required parameters including the
length of the semi-major axis and amount of flattening in the reference ellipsoid, and
the translation, rotation, and scale between the user defined system and WGS-84.
To use this datum for the position computation and measurements, use the $PASHS,DTM,USR
command after defining the datum parameters.
40
Table 4.6: External Frequency Parameters
Parameter
Input impedance
Frequency range
Lock range
GG Surveyor GPS+GLONASS Reference Manual
Specifications
50 ohms
10 KHz to 21 MHz in
10KHz increments
± 5 ppm
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