Question about system noise figure calculation when every block noise figure is known

[hmsheng]

If the noise figure of each block in the receiver is known, we can calculate the total noise figure of the system with the cascade noise figure formula. The calculation is based on the condition that all the blocks are matched to 50 Ohm. But this is not the fact! So the calulated result should be no sense.

Any comment on my viewpoint?

 

[Hunter_BJUT]

system noise figure

I don't think so.
the input is terminated in 50 ohms, the kTB noise level at room temperature in a 1 Hz bandwidth is –174 dBm, so it will affact NF values.
but the system NF is determined by Friis equation.
if you use 75ohm system maynot be -174dBm BW, but sys NF should change accordingly.