8163A/B, 8164A/B, 8166A/B User’s Guide 233Setting Attenuation and/or Power Levels 8How to Use the Power Control Feature81576A/77A Attenuator modules incorporate Power Control functionalitythat automatically corrects for power changes at its input to maintain yourdesired output power.This feature is designed to compensate, for example, for output power driftby the source.When Power Control is On:• If P actual deviates by more than 0.1 dB from your desired P SET value,the Attenuator module automatically restores P SET at the maximumpossible filter transition speed of 12 dB/s.• Input power is measured using your set Averaging Time.• To avoid ‘hunting’, and consequent wear on the filter motor mechanismin response to an unstable source, for differences between P SET andPactual greater than 0.01 dB, but less than 0.1 dB, P SET is updatedapproximately every 30 s.• The Attenuator module does not respond to a power difference of0.01dB or less. Such a change is regarded as noise.• If the attenuation is driven beyond 0 dB, Exp (“Excessive Power”) isdisplayed. There is now insufficient input power for the Attenuator tomaintain your desired P SET.Power Control On/OffTo enable or disable Power Control, select the [Pwr Ctrl] parameter.When Power Control is On the Attenuator’s status display includes ‘PC’.The Menu item <Pwr Control> is functionally equivalent to the[Pwr Control] parameter.Attenuator Menu Options81570A/71A/73A Menu OptionsPress the [Menu] softkey to display the window shown in Figure 141 onpage -234.
