4. ALC

When an M9381A PXIe Vector Signal Generator is connected, you will see the display as below:

When an M9383B/M9384B/M9484C is connected, you will see the display as below:

ALC Auto

(M9383B/M9384B/M9484C only)

Choice: On | Off

Default: On

Enables or disables ALC On and ALC Bandwidth couplings.

For IQ modulation, ALC Auto and Power Search Auto should be On.

ALC

Choice: Off | On

Default: On

Double-click or use the drop-down menu to enable or disable the automatic level control.

On – The ALC circuit constantly monitors and controls the output power level.

Off – No automatic leveling occurs.

ALC Bandwidth

Choice: Auto | PXI0 | ... | PXI7

Default: Auto

Double-click or use the drop-down menu to select a bus for ALC hold signal path on PXI backplane.

This parameter is not available for all instrument models and may be greyed out or not shown in GUI.

ALC Trigger Source Bus

Choice: Auto | 200 Hz | 2 kHz | 20 kHz

Default: Auto

Double-click or use the drop-down menu to select an ALC bandwidth. Auto means the signal generator automatically selects the optimized bandwidth for the current signal setup.

This parameter is available when M9381A PXIe Vector Signal Generator is selected in the system configuration.

ALC Hold Mode

Choice: Off | Track on Marker | Hold on Marker

Default: Track on Marker

Double-click or use the drop-down menu to select how the ALC circuit in the output module functions when the ALC is enabled.

Off − ALC hold is turned off.
Track on Marker − When playing a waveform file and a Marker is crossed in the waveform file, the ALC will track on the Marker.
Hold on Marker − When playing a waveform file and a Marker is crossed in the waveform file, the ALC will hold on that Marker

This parameter is available when M9381A PXIe Vector Signal Generator is selected in the system configuration.

Power Search Reference

Choice: RMS | Fixed | Modulated

Default: RMS

Double-click or use the drop-down menu to select one of the following reference signals when doing a power search.

RMS – Power search uses a DC bias value equivalent to the value derived from the file header or the calculated value from the current I/Q data.

Fixed – Power search uses a fixed 0.5 V reference.

Manual – Power search allows the user to specify the DC bias voltage.

Modulated – Power search uses the AC bias from the actual modulating signal.

This parameter is not available for all instrument models and may be greyed out or not shown in GUI.

RF During Power Search

Choice: Normal | Minimum

Default: Normal

Double-click or use the drop-down menu to select the level of the output power control during a power search routine.

Normal – Performs power searches without setting the internal step attenuator to its maximum setting. Glitches and power changes may be present during the search.

Minimum – Sets the signal generator's step attenuator to its maximum setting during power search to protect sensitive circuits.

Set ALC to Off to enable this parameter.

Power Search Auto

(M9383B/M9384B/M9484C only)

Choice: On | Off

Default: On

Toggles Power Search Mode between On or Off.

When enabled, power search calibration routine is executed whenever an instrument setting is modified. This includes changes to frequency, amplitude and modulation.

For IQ modulation, ALC Auto and Power Search Auto should be On.

For M9383B/M9384B/M9484C, this parameter is grayed out and set to Very Slow when ALC Auto is On.