250 Keysight N9938-90003 User’s Guide
System Settings
System Configuration
GNSS and GPS Freq Ref Source Settings
For convenience, the GNSS Settings menu includes the Freq Ref Source
softkey.
—Press System
> System Configuration > GNSS (GPS+) > Freq Ref Source
[GPS] then
— Choose one of the following:
— Int
, Ext, or GPS
For more, on the Freq Ref Source softkey choices, refer to “Frequency
Reference Source” on page 250.
Frequency Reference Source
The FieldFox internal frequency reference source is used to make accurate and
stable measurements. To improve measurement accuracy and stability, you
can use a highly-stable external 10 MHz reference source or a precision timing
signal provided with Built-in GPS (Opt. 307).
The Frequency Reference setting will survive a Factory Preset or Mode Preset
and is saved as part of the Instrument State. When resuming after Standby, the
FieldFox will display an Unlock message while it acquires a lock to an external
or GPS source.
How to select Frequency Reference Source
—Press System 7 > System Configuration > Frequency Ref > Freq Ref
Source
— Then choose from the following:
— Int
Internal frequency reference
— Ext
External frequency reference. Connect the 10 MHz External
Reference to the Ref In/Trig In SMA (f) connector on the FieldFox top
panel. The FieldFox may take up to 10 seconds to lock to a valid
External Reference source
— GPS
Available ONLY with Built-in GPS (Opt. 307). When selected, the
internal GPS is immediately enabled and a search for satellites
begins. When satellites are found, the precision timing signal is NOT
used directly, but is used to correct the absolute frequency of the
internal reference many times per second.
Hold-over mode
When the GPS signal is lost, the last GPS reading is used as a hold-over
correction value for the internal reference. The hold-over correction value is no
longer used, but instead the factory-set correction value is used, when any of
the following occur:
— when GPS is disabled.
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