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PNA-X Measurement uncertainty for transmission

Question asked by MFinner on Feb 25, 2011
Latest reply on Mar 2, 2011 by MFinner
Hello VNA team,

for quite a while I am trying to understand how the transmission uncertainty is to be calculated for our PNA-X VNA.
I saw in this forum that you are usually referring to document "08720-90393" for questions about VNA measurement
analysis. I have tried to use the datasheet in combination with the formula provided in your reference document.
However the results do not seem to be useful. I specially realized that when I was trying to compute the phase uncertainty
which fails due to an argument being larger than "1". Basically the error part computed is always smaller (about one
order of magnitude) as compared to the "real" S21. Hence Etm/S21 leads to some value >1.
I have used linear values for the effective system data, however, I think that my problem is the conversion of the
trace noise as well as the noise floor values to linear quantities.
I have used  the following calculation PnoiseflorLIN = 10^(NoisefloordB/10) * 0,001 and TracenoiseLin = 10^(TracenoisedBrms/20) - 1
Is this correct or am I doing a mistake here. The order of magnitude for the systematic error seems to be ok, so probably
it is only an error in the noise calculation. (BTW, I calculate the crosstalk contribution as follows XTalkLIn = 10^(XTalkdB/20)).
If this is ok so far, do you have an idea what can lead to the calculation error for the S21phase part? Am I probably missing any
required normalization?

Thanks very much for your help.
MFinner  

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