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noise figure at different frequencies

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jmpac

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How to calculate noise figure for frequency F1 in the following system?

RXin@F1 -> LNA -> MIXER1 -> AMP@F2 -> MIXER2 -> DRIVER -> TXout@F1

F1 es the same frequency for RXin and TXout.

Mixer1 downconverts F1 to F2 (intermediate frequency), and Mixer2 upconverts F2 to F1, where F2<<F1

How is Friis Formula applied, since gain for AMP is different for F1 and F2?

Thanks in advance.

Jose
 

Hi,
If GAIN is different at f1 and f2, you have to considere to different amplificator with two different gain and the same Noise Factor.
Noise is transpose by the mixer like signal frequency.
That's all.
 

With your system there is no problem with Friis' formula to calculate noise figure. In mixers use conversion loss, the IF frequency does not matter.
Make sure the second (upconverting) mixer is linear as Friis' formula only holds for linear circuits.
 
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For Mixers, F is defined as..

F=(S/N@Input)/(S/N@Output) so frequency conversion is included.
 
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