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PNA-X OIP3 measurement (weird shape at 500MHz) - need help

Question asked by cclim2011 on Nov 23, 2011
Latest reply on Nov 23, 2011 by Dr_joel
Hi there,

I am using the PNA-X N5242A to measure a DUT's OIP3.
I use levelling (DUT output at 5dBm). DUT gain about 16dB.
I set different receiver attenuation level. At setting at about 25dB/30dB attenuation (ie ~-20dBm/~25dBm power hitting the PNAX receiver mixer).
There is always an odd shape at about 500MHz. Please refer the graph of two units' measurement at receiver attenuation setting of 25,30,35,40dB.

Can anyone enlighten me if this is due to the NA or the DUT? Any means to verify? How do I know which attenuation level is the correct OIP3 reading? The higher the better?

Thanks.  

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