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E8257C/D Narrow Pulses

Question asked by Andrew004 on Apr 20, 2017
Latest reply on May 9, 2017 by Andrew004

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Hi Keysight,

I have a question on the ALC/Power search feature. We've been having some trouble with narrow, pulsed signals after installing a f/w update on our sig gen's. This datasheet sets the min p/w with ALC at 1 microsecond. My question is, do the power search and ALC features require some sort of settling time? Are there any preconditions we have to take into account before providing our UUT the pulse? Another question is, if we set the power accurately in CW and then switch to pulse, how critical is ALC or power search?

D's F/W: C.06.21

C's F/W: C.03.23

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thysell Apr 26, 2017 1:00 PM
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Hi,

The ALC can work with pulses as narrow as 1 us. Power search disables the pulse modulation and enables the ALC. Both cases require a certain amount of time to reach the desired level. If this time is 1 ms, then it would take one thousand 1 us pulses to reach the desired level.The settling time is dependent on two things:
1.) The difference between the current level and the desired level
2.) The ALC bandwidth. (100 Hz, 1 kHz, 10 kHz, 100 kHz)

Setting the ALC bandwidth to the largest value, 100 kHz, will reduce the time required to reach the desired level.

I'm not exactly sure why a firmware upgrade would change this behavior but it is definitely possible. It may have to do with improved calibration routines or leveling algorithms. It might be possible that the firmware upgrade reset the ALC bandwidth to a value narrower than what you were using.

If you set the power in CW mode you have probably already provided the ALC enough time to level.
NOTE: I don't remember if the RF output must be on for the ALC to level.
Enabling pulse modulation without changing the RF Amplitude should have the instrument at the correct level and the pulses will be at the desired level with no waiting.

Keeping the ALC enabled, even with pulsed signals, means you are less susceptible to long term amplitude drift.

Changing the RF Amplitude while generating pulsed signals will require a certain amount of time (number of pulses) to reach each new level assuming the ALC is on.

Hope this helps
Pete
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- Andrew004 @ thysell on Apr 30, 2017 9:08 AM
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  Hi Pete,
  
  Thank you for the reply. We looked into it some more on Friday and were able to set up our test with all the needed parameters using ALC. We believe the issue could be that when we adjust the "delay after a trigger" setting, the pulse does not generate on single or even multiple triggers. We had to provide a continuous set of triggers first before the sig gen would become operational. After a series of continuous triggers were provided to the sig gen, it would then be functional with single triggers. This would not occur on the old f/w. We could adjust our delay setting and the sig gen would be functional right away. Has something like this ever come up? If so, is there a refresh or some other type of command that we could provide to kind of jump start the sig gen with the new setting?
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  - thysell @ Andrew004 on May 2, 2017 8:26 AM
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    Hi Andrew003,
    
    Could you provide the Firmware version that you were using that worked correctly and the version that you upgraded to?
    Unless you need something in the new version of firmware it is always possible to roll back to the previous version of firmware.
    With the firmware revision information, I will log the problem you are experiencing and the firmware team should be able to look at it.
    
    Thanks for your help
    
    Pete
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    - Andrew004 @ thysell on May 9, 2017 5:00 AM
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      Okay I'll see if that's a possibility.
      
      Old, working version F/W: C.03.23
      Newer version F/W with issue: C.06.21
      
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E8257C/D Narrow Pulses

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