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Noise figure of a VNA

Question asked by RadioRon on Oct 4, 2012
Latest reply on Oct 11, 2012 by drkirkby
I'm interested in knowing the noise figure of a VNA.  Let's use the the E5071B as an example.  I understand that the front end consists of the input port followed by a directional coupler and then to a receiver.  I presume the receiver first stage is a broadband mixer.  I don't know what the coupling coefficient of the directional coupler is, but I presume it is a lower loss type, like 10 dB or less, for best directivity.  So, I would estimate the noise figure to be the sum of 10 dB plus the receiver noise figure of, let's say, another 10 dB for a total of 20 dB.  Fudge in some additional losses and it might be 25 dB.  Does anyone out there have a better idea?