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913
Common Measurement Functions
FREQ Channel
Couplings: In the Spectrum Analyzer, the four parameters Center Freq, Start Freq, Stop
Freq and Span are interdependent, as changing one necessarily affects one or
more of the others. The couplings between Center Freq and Span are detailed
under the key descriptions for those keys. These couplings also affect Start
Freq and Stop Freq.
You cannot set Start frequency = Stop frequency. You cannot select zero span
by setting Start = Stop. The instrument will alter the value of the last setting to
maintain a minimum value of 10 Hz for the difference between Start and Stop.
Preset: Start Freq does not preset. On Mode Preset, Span & CF preset, and Start Freq
is derived. On a Meas Preset only Span presets, CF does not, so Start Freq will
vary depending on CF.
When a Mode Preset is performed while in External Mixing, the Start
frequency of the current Mode is set to the nominal Min Freq of the lowest
harmonic range in the Harmonic Table for the current mixer setup.
If the current measurement has a limited Span available to it, and cannot
achieve the Span shown in the table (Span=Stop Freq – Start Freq), the
analyzer uses the maximum Span the measurement allows, and sets the Center
Freq to the midpoint of the Start and Stop Freq values in the Harmonic Table.
Thus, in this case, the Start Freq will preset to a frequency below the preset
Center Freq by ½ of the maximum Span.
When Restore Input/Output Defaults is performed, the mixer presets to the
11970A, whose Start frequency is 26.5 GHz.
Therefore, after a Restore Input/Output Defaults, if you go into External
Mixing and do a Mode Preset while in the Spectrum Analyzer Mode, the
resulting Start Freq is 26.5 GHz.
State Saved: Saved in instrument state
Min: –80 MHz, unless Source Mode is set to Tracking, in which case it is limited by
the minimum frequency of the Source
If the knob or step keys are being used, depends on the value of the other three
interdependent parameters
While in External Mixing, the minimum Start Freq you can set is determined
by the external mixing parameters. It will be close to the minimum LO
frequency (3.8 GHz if undoubled, 8.6 GHz if doubled) times the harmonic
number, for the lowest harmonic range in the Harmonic Table for the current
mixer setup. It can be queried with the SCPI command :FREQ:STARt? MIN.