mona123
Member level 5
Hi, If I connect a long lossy transmission line to the output of an amplifier and measure the noise output power, will my measured noise power be shaped by frequency response of transmission line? Thanks.
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Sure but it has a low pass filter characteristic. But if you have a high gain amplifier the influence is quite small.
Thanks John. So if I measure lets say -100 dBm output noise power @1GHz at the output of the die and I have cable loss connected at the output of die of 3dB @1GHZ. Then the output noise power measured using cable would be -103 dBm?
One more confusion related to this is that why do we have noise figure of a passive device equal to loss of passive device, if the signal and noise both will be attenuated by same amount? won't the signal to noise ration at the input will be equal to signal to noise ratio at the output, hence noise figure unchanged. I am sure I am missing something big here?
Thanks
Thanks. So does it mean its opposite. I will have 3dB more noise power that means I should measure -97dBm in the earlier example I gave? I am confused...I want to understand only in terms of noise power not noise figure..
"does noise attenuate like signal through a transmission line "
Lets take example where G is small. let say Noise power is -164dBm and is passing through same 3dB transmission loss. what is the effective noise power at this stage? it is not -167dB am sure.
if you find the answer means you understood noise power and hence noise figure calculations.
Hope this trigger your thoughts.