How to mesure noise figure without noise generator on AD FMCOMMS2?
You can use the gain method. For this measurement you need to know the gain, bandwidth and system characteristic impedance.
NF = Pn - (-174dBm/Hz + 10LOG10(BW) + GAIN)
To determine Pn you would terminate the input in characteristic impedance (50ohm) and measure Pn at the output.
The issue with this method is that it will be as accurate as the gain and BW numbers used.
Pn is noise power density (in dBm/Hz)? Could you tell, how to calculate Pn knowing the average noise level (on the screen IIO Oscilloscope)?
Or is it included in Pn-10LOG10(BW)?
You would have to capture the data and do the computation in some other tool. To arrive at absolute signal levels you need to know that 0dBFS is 0.625Vpk.
Pn has units of dBm/Hz. In your case, once you perform the calculation in a certain bandwidth you will have power (Pncalc) in absolute units [dBm] provided you use 0dBFs = 0.625Vpk relationship). NF = Pncalc -174dBm/Hz - Gain
Could you recommend some tools for capture the data and computation?
Do you know what window function are used in IIO Oscilloscope?
My understanding is Pncalc is absolute noise power. So we need to convert it to noise density. NF = Pncalc-10log10(BW)-Gain+174
So you are saying 0 dBFS is 0.625 vpk. So 0 dBFS in absolute power, if we do the math and assume zin=50 ohm, comes to -0.10 dBm.
Now when I terminate the RF input with 50 ohms and measure power, How can I estimate the absolute power of this quantity? I mean how do I know how much dBFS this is?