Trace noise and noise floor

[Frans Verbeyst]

During the VNA Tools II it was explained how to characterize the "trace noise" and "noise floor" of a VNA device.

Would it be possible to shortly explain the meaning, origin and subtle difference between both ?

I also have a question with respect to normalization of the measured noise floor (setting the test port power to the preset value) to 0 dBm.

Suppose the test port power is preset to e.g. -15 dBm (probably corresponding to the most optimal setting of the hardware), doesn't the above assume that normalizing (moving) to 0 dBm has no negative impact on the noise floor, while in practice (selecting 0 dBm test port power) it could?

Thanks,

Frans

[Michael Wollensack METAS]

Hi Frans,

the trace noise and noise floor is a model to describe the noise of VNA measurements.

The noise floor is independent of the measured power at a receiver. And the trace noise get's multiplied by the by the received power.

The origin for noise floor could be thermal noise. The origin of the trace noise could be the noise on the source signal of the VNA. E.g.: When measuring a short you see more noise on the data than measuring a load.

Normalization:

Today I would propose. Do the noise floor characterization at the power level you want to make all your measurement (e.g.: -15 dBm) and do not normalize it to 0 dBm. The normalization is only needed if you want to compare different VNAs with different power levels.

Hope this helps.

Regards

Michael