37 lines
830 B
Markdown
37 lines
830 B
Markdown
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---
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title: NF噪声系数
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updated: 2022-05-16 12:05:57Z
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created: 2022-01-08 13:17:43Z
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tags:
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- nf
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- 混频
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- 级联
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---
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# 原理
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$-174+10*log(BW)+G+NF=P_f$
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$P_f$为输出噪底，G为DUT增益，等于Po-Pi，带入上式得
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$NF=P_f-(-174+10*log(BW)+G)$
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BW=10k，Pi=-100dBm时，=Pf-Po+30
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频谱仪自身NF时，G=0
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前置放大器得噪声系数NF+增益G，比频谱仪噪声系数$NF_{sa}$大15dB以上时
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# 级联
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级联时最后一级的噪声系数对总体噪声有贡献，==增益则没有==，
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比如前级只算到混频器，总体噪声系数==并不会==因为混频器的插损而下降
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混频器之后需要加放大器对增益进行补偿
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对于接收前端，需在混频器之前达到预期的噪声系数，否则随着后级权重的降低噪声系数就更难达到；
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#nf
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#级联
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#混频
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