6 Input/Output
6.6 Freq Ref Input
External
The external reference is used.
Pulse
The internal reference continues to be the frequency reference for the instrument in
that it determines the reference contribution to the phase noise, but its average
frequency is adjusted to follow the 1 pps signal at the EXT REF IN input. Therefore,
the instrument frequency accuracy will be dominated by the aging rate of the 1 pps
signal instead of the aging rate of the internal reference, except during the time it
takes to lock to a new 1 pps signal, approximately 10 minutes.
Sets the System, Alignments, Timebase DAC setting to “User”. This setting survives
Preset and Power Cycle, but it set to “Calibrated” on a System, Restore Defaults,
Align or a System, Restore Defaults, All
When a 1 pps signal is present at the EXT REF IN input, and either Pulse or Sense is
selected, the internal reference frequency is affected by this signal; in effect, it
“learns” a new accuracy setting. This setting can be seen by going to the System,
Alignments, Timebase Dac menu, and looking at the User key in that menu. You will
note that User has become automatically selected, and that the value shown on the
User key is the updated value of the timebase DAC as “learned” from the 1 pps
signal. Note that this replaces any value the user might have previously set on this
key.
Once the setting is learned the user may remove the 1 pps signal; the User setting
for the Timebase DAC is retained until you manually select “Calibrated” or execute a
System, Restore Defaults, Align or a System, Restore Defaults, All. If you want to
make the User setting permanent there is information in the Service Guide that tells
you how to change the Calibrated setting of the Timebase DAC.
Note also that if the 1 pps signal is removed when Sense is selected, the instrument
will simply switch to the normal state of the Internal reference and display
SENSE:INT in the Settings Panel. However, if the 1 pps signal is removed when
Pulse is selected, the instrument will generate an error
The J7203A Atomic Frequency Reference is an accessory for the X-Series Signal
Analyzer that provides a highly accurate 1 pps timebase to use in conjunction with
the Pulse setting. With the J7203A, the 1 pps signal is guaranteed to meet the input
requirements of the EXT REF IN port, and the improved accuracy of the instrument’s
internal frequency reference is specified. This is the only 1 pps signal that is
guaranteed to function properly with the X-Series.
2452 Spectrum Analyzer Mode User's &Programmer's Reference
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