Noise Figure (NF)
Noise Figure tells us how much noise a system adds to a signal.
\[
F = \frac{SNR_{in}}{SNR_{out}}, \quad
NF = 10 \log_{10}(F)
\]
Lower NF = Better receiver
Higher NF = More noise added
Higher NF = More noise added
Example 1 (dB Form)
Given:
Input SNR = 20 dB
Output SNR = 15 dB
Input SNR = 20 dB
Output SNR = 15 dB
Step 1:
\[
NF = SNR_{in} - SNR_{out}
\]
\[
NF = 20 - 15 = 5 \, dB
\]
Final Answer: NF = 5 dB
Meaning: The receiver reduces SNR by 5 dB due to added noise.
Example 2 (Linear Form)
Given:
Input SNR = 100
Output SNR = 25
Input SNR = 100
Output SNR = 25
Step 1:
\[
F = \frac{100}{25} = 4
\]
Step 2:
\[
NF = 10 \log_{10}(4) \approx 6 \, dB
\]
Final Answer: NF ≈ 6 dB
Summary
Noise Figure = Loss in SNR caused by the system
\[
NF (dB) = SNR_{in} - SNR_{out}
\]
- NF measures receiver performance
- Lower NF ⇒ Better system
- Higher NF ⇒ More noise added
Noise Figure determines how well a receiver can detect weak signals.