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Question: measure P1dB with ENA E5071C option 280

Question asked by tomato on Jan 12, 2010
Latest reply on Jan 14, 2010 by tomato
hello everyone
Here's the idea.
I have set a marker at 500MHz, Pin is set at -25dBm, obtain the gain.
I changed the Pin into -20dBm. As a result, the Gain will drop for sure.

1st question: Do I need to calibrate every time i change the Pin, as the Pin is no longer -25dBm??

If calibration is not necessary
I keep on increasing my Pin (from -25dBm into -10dBm), until the Gain is drop 1dB from the 1st reading (Pin = -25dBm).
Now, I have obtained the latest Gain, and also the Pin.
Gain = Pout - Pin
Therefore i get the Pout, as it is also the P1dB point.

2nd question: Is this concept acceptable? Is it correct?

If it is correct
3rd question: (For my case) Why i can't get the correct P1dB result? ?
The power out is different from what i obtain from my P1db testing station.
For my case, P1db point is decreased from -0.5dBm into -1.7dBm.
During my P1dB testing station, the Pin = -0.5dBm and Pout is 18.93dBm.
But by using this method, what i get is Pin = -1.7dBm and Pout is 18.938dBm.

Do i make a mistake during this process?
Am i missed something important?
Hope you all can understand what i trying to say here.  

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