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LTE burst signal - my power level is off

Question asked by tabbott Employee on Jan 21, 2010
Latest reply on Apr 22, 2010 by tabbott
I have generated a bursty LTE waveform in Matlab and downloaded this waveform into my  Agilent MXG N5182A vector signal generator.  However, when I play this waveform out on the MXG the RF output power for each burst is off by several dB.  Why is this and how can I fix it?

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The reason why the signal off is that the MXG  has and Automatic Level Control (ALC) loop for stabilizing output power over time and temperature. By default the ALC expects a continuous waveform.  If the waveform is bursty (has long Off time vs. On time) the ALC will overcorrect during the off portion of the burst.  When the ON portion of the burst finally arrives it can generate a significant amount of overshoot depending on the duty cycle of the signal. There are two ways to fix this.
1)     Turn the ALC off and set the power search reference to RMS. See MXG users guide for more details.
2)     Create a “Marker” file that runs in parallel with your waveform that follows the same power envelope as your waveform. This can be downloaded into the MXG together with your waveform.   After downloading, the marker file signal can be routed to the internal ALC hold function available in the MXG.  By performing this step the ALC loop will only level over the ON portion of the burst and the rms RF output power level will perfectly follow the MXG front panel settings. See MXG users guide for more details.
Helpful references:
MXG Users guide: http://cp.literature.agilent.com/litweb/pdf/N5180-90003.pdf(See section 7  “ Using Waveform Markers” page 155)
MXG/ESG/PSG Creating and Downloading Waveform Files:  http://cp.literature.agilent.com/litweb/pdf/E4400-90627.pdf

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