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Old 2-Dec-2013, 8:07 PM   #1
mmbridges
Junior Member
 
Join Date: Nov 2013
Posts: 8
Noise Figure Accounting

I am trying to understand how the addition of a low noise figure (NF) preamp can improve the overall system NF.

I have a Zenith DTT-901 Set Top Box (STB) that I cannot find the NF for so it so lets assume it is 6dB.

What is the formula that shows how the gain and NF of a preamp improve the overall system NF when placed in front of the STB. (this assumes the preamp NF is lower than the STB NF)

I have read that as long as the preamp gain (dB) is sufficiently larger than the STB NF (dB) then the over all system NF (dB) will be determined by the pre-amp NF (dB).

I am an equations kind of guy so would like to see exactly how as the pre-amp gain increases the system NF approaches the pre-amp NF.

Thanks!
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