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78 Chapter 2
Using System Features
Using System Configuration and Alignment Keys
Align Subsystem - Allows you to activate one or a group of the
standard internal instrument alignments. Perform alignments on
circuitry relating to the following internal alignments. Press the
ESC
key to cause any alignment to stop.
Align RF - Activates an alignment on the RF circuitry.
Align IF - Activates an alignment on the IF circuitry. The main
gain of the Analog IF is used to compensate for prefilter BW gain
variations so the gain of the entire IF path before the A/D
remains constant.
Align ADC - Activates an alignment on the ADC circuitry.
Align 50 MHz Reference - Enables a service technician to
adjust the amplitude of the internal 50 MHz reference signal for
absolute amplitude accuracy. The test equipment and the
adjustment procedure required are described in the E4406A
service guide.
NOTE The Align 50 MHz reference feature can only be activated if you have a
service password. The password is not available unless the user has
purchased the service guide.
Align Current IF Flatness - Activates an immediate
measurement of the current IF flatness, for FFT spectral
amplitude compensation. Normally this alignment occurs in the
background when the instrument bandwidth is changed. Given
the current BW and Gain DAC settings for a measurement,
alignment is done using the comb calibration signal. The relative
amplitude of combs within the BW are compared to expected
amplitudes to generate the effective shape of the current IF path.
If Time Corrections are active, this alignment generates complex
IF responses (magnitude and phase) rather than just the original
scalar (magnitude) response. The complex alignment requires
reasonable delay estimation, and improved trigger compensation
so the phase response of several averaged measurements can be
unwrapped properly.
Align Current SysGain - Activates a fine-tuning adjustment of
the system gain. This is done by measuring the response of the
current system state configuration to the 50 MHz amplitude
reference signal. All subsequent measurements are then
compensated appropriately for absolute amplitude accuracy.
Normally this occurs in the background when the instrument
bandwidth is changed.