4. ALC

ALC

Choice: On | Off
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

Select the ALC loop bandwidth from the drop-down list. Choose Auto to let the signal generator automatically select the optimized bandwidth for the current signal setup.

For waveforms with varying amplitudes, a high crest factor, or both, set the ALC loop bandwidth to 100 Hz, which is the default bandwidth set when an ARB format is turned on. Limiting the loop bandwidth of the ALC circuit prevents the ALC from sampling the fast rising edges of high-crest pulsed waveforms.

Attenuator Hold

Double-click or use the drop-down menu to enable or disable the signal generator’s attenuator hold function.

• On − locks the attenuator at its current setting to prevent glitches. Use this function to prevent power discontinuity normally associated with the attenuator switching during power adjustments.

• Off − leaves the attenuator in a dynamic state. Setting the amplitude also sets the ALC level and the attenuator.

Attenuation

Range: for specified range values, see the signal generator's data sheet

Enter a value for the output attenuator. The maximum ALC Level is not available for all attenuator settings. Changing the amplitude or ALC level causes the other parameter to change by an equal amount. Choose the ALC level and attenuator value to keep the ALC at its most effective level.

Set Attenuator Hold to On to enable this parameter.

ALC Level

Range: for specified range values, see the signal generator's data sheet

Enter a value for the ALC output power level.

Set Attenuator Hold to On to enable this parameter. The ALC Level is set automatically by the Amplitude parameter when Attenuator Hold is Off.

Power Search

Choice: Manual | Auto | Span
Default: Auto

Select the power search mode from the drop-down menu.

• Manual – power search runs with each press of the Power Search button.

• Auto – power search automatically runs with each change to the RF frequency or power, or with each change to the I/Q modulation state.

• Span – power search over a range of frequencies, save these values and use them while the signal generator is tuned over the specified frequency range.

Set ALC to Off to enable this parameter.

Power Search Reference

Choice: Fixed | Modulation | RMS | Manual
Default: Fixed

Set ALC to Off to enable this parameter.

Double-click or use the drop-down menu to select a fixed or modulation reference signal when doing a power search.

• Fixed − power search uses a fixed 0.5 V reference.

• Modulation − power search uses the RMS value of the current I/Q modulation as the reference.

• RMS – power search uses the RMS level specified in the waveform header when doing a power search. (Internal Arb only)

• Manual – power search uses the voltage level specified in Manual Power Search Level.

Power Search Manual Level

Set the voltage level used as the power search reference when the reference type is set to Manual. Setting this voltage is equivalent to varying the waveform RMS voltage and is used to provide a DC bias on the I/Q modulator that approximates the level of the modulating voltage. This parameter can be used with Wideband IQ modulation and bursted signals.

Set the Power Search Reference to Manual to enable this parameter.

RF During Power Search

Choice: Normal | Minimum
Default: Normal

Set ALC to Off to enable this parameter.

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.

External ALC Hold

Choice: On | Off
Default: Off

Double-click or use the drop-down menu to enable or disable the External ALC Hold input. Not Available on the ESG or MXG.