RF chain
Noise, Noise Figure and G/T Calculator
Refer noise to an input plane and evaluate receiver sensitivity.
Enter the design inputs, then calculate to inspect the results.
Swipe the diagram sideways to see the full view. With a keyboard, focus the diagram and use the arrow keys.
Understand the system
Thermal noise and bandwidth
Available thermal noise is kTB. Noise density is kT, independent of chosen bandwidth. The final’s 27°C means 300.15 K, giving about −129.06 dBW or −99.06 dBm over 30 MHz. A factor-ten bandwidth increase adds 10 dB noise.
k: J/K; T: equivalent system K at stated reference plane; B: noise bandwidth in Hz; N: W; N_0: W/Hz.
Do not substitute Celsius in kTB.
Source: finalExam.pdf · PDF page 4
Common mistakes
- Distinguish standard T₀, physical temperature and equivalent added temperature.
- Linear gain 20 is 13.01 dB, not 20 dB.
- dBm equals dBW + 30.
Formula reference and symbol definitions
Thermal noise
N: W; k: J/K; T: K; B: Hz
Available thermal noise, equivalent bandwidth.
Example: At 300.15 K and 30 MHz, N = 1.38 × 10⁻²³ × 300.15 × 30 × 10⁶ ≈ 1.243 × 10⁻¹³ W = −99.057 dBm.
Open related tool →Noise density
N_0: W/Hz; T: K
Thermal noise model.
Example: At 290 K with k = 1.38 × 10⁻²³, N₀ = 4.002 × 10⁻²¹ W/Hz ≈ −203.98 dBW/Hz.
Open related tool →Noise factor
SNR values: linear power ratios
Standard reference source temperature.
Example: If input SNR is 100 and output SNR is 50 (both linear), F = 100/50 = 2.
Open related tool →Noise figure
NF: dB; F: linear
F ≥ 1.
Example: For F = 2, NF = 10 log₁₀(2) ≈ 3.010 dB.
Open related tool →Equivalent noise temperature
T_e,T_0: K
T₀ = 290 K.
Example: For F = 2 at T₀ = 290 K, Tₑ = (2 − 1) × 290 = 290 K.
Open related tool →Passive device noise
L: linear loss; T_p: physical K
Passive attenuator; input reference plane.
Example: For linear loss L = 2 at physical temperature 290 K, Tₑ = (2 − 1) × 290 = 290 K.
Open related tool →Cascade equivalent temperature
T_i: K; G_i: linear power gains
All temperatures referred to stage inputs.
Example: For T₁ = 100 K, G₁ = 10, T₂ = 200 K, Tₑ,total = 100 + 200/10 = 120 K.
Open related tool →Friis noise factor
F_i,G_i: linear
Common reference temperature.
Example: For F₁ = 2, G₁ = 10 and F₂ = 3, Ftotal = 2 + (3 − 1)/10 = 2.2 ≈ 3.424 dB.
Open related tool →Receive G/T
T_sys: K
Gain and temperature at same plane.
Example: For gain 44 dBi and Tsys = 300.15 K, G/T = 44 − 10 log₁₀(300.15) ≈ 19.227 dB/K.
Open related tool →