Noise figure formula

Discussion in 'Wireless & RF Design' started by donut, May 24, 2012.

  1. donut

    Thread Starter Member

    May 23, 2012
    51
    0
    Wikipedia says NF = 10 log ( SNRin / SNRout) = SNR in - SNR out. My question i guess is more mathematical relating to how SNRin - SNRout was derived.

    Please advise.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    You have misquoted Wikipedia slightly.

    It actually says
    [​IMG]

    The derivation would be in complete form

    NF=10log\( \frac{SNR_{in}}{SNR_{out}}\)=10log(SNR_{in})-10log(SNR_{out})=SNR_{in,dB}-SNR_{out,dB}

    remembering that in general

    log(\frac{A}{B})=log(A)-log(B)
     
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,650
    632
    And the SNRin and SNRout figures are measurements, not derivations.
     
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