C/N ratio in CATV System design
时间：04-11
整理：3721RD
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Hi Everyone,
I need help concerning CATV specifications. I crossed upon the C/N ratio and it's use in CATV system design. C/N of and amplifier means the ratio of Carrier to the output noise of it. For one unit this definition is fine, but what about a cascade of amplifiers ?
In ordinary RF cascade design, one wants to calculate the degraded noise figure, need to calculate the whole cascade NF with the well known formula :
F1+(F2-1)/G1+?.
But in CATV they are summing the inverse of the C/N linear ratio :
C/Ntotal [dB] = -10log ( 10^(-C/N1/10)+ 10^(-C/N2/10)+ 10^(-C/N2/10))
C/Ni is the C/N ratio of a stand alone function.
Can any one tell me what is the justification of the formula ? It rejects the ordinary NF formula we all learned !
I need help concerning CATV specifications. I crossed upon the C/N ratio and it's use in CATV system design. C/N of and amplifier means the ratio of Carrier to the output noise of it. For one unit this definition is fine, but what about a cascade of amplifiers ?
In ordinary RF cascade design, one wants to calculate the degraded noise figure, need to calculate the whole cascade NF with the well known formula :
F1+(F2-1)/G1+?.
But in CATV they are summing the inverse of the C/N linear ratio :
C/Ntotal [dB] = -10log ( 10^(-C/N1/10)+ 10^(-C/N2/10)+ 10^(-C/N2/10))
C/Ni is the C/N ratio of a stand alone function.
Can any one tell me what is the justification of the formula ? It rejects the ordinary NF formula we all learned !