How to Use Noise Figure Calculator
The Noise Figure Calculator supports two modes: Basic (single-component analysis) and Cascade (multi-stage system using the Friis formula).
Basic Mode
- Select Basic mode using the mode toggle.
- Enter the Input SNR (SNR_in) — the signal-to-noise ratio at the input of the device. Choose dB or linear units from the dropdown.
- Enter the Output SNR (SNR_out) — the SNR at the output.
- The Noise Figure Calculator computes the Noise Factor F = SNR_in / SNR_out and the Noise Figure NF = 10 × log₁₀(F) in dB.
Cascade Mode (Friis Formula)
- Select Cascade mode.
- Enter the Noise Figure (NF in dB) and Gain (dB) for each stage.
- Add or remove stages using the ”+ Add Stage” button.
- The Noise Figure Calculator applies the Friis formula to compute the total system noise figure.
- The breakdown table shows the individual F contribution from each stage so you can identify the dominant noise source.
Formula & Theory — Noise Figure Calculator
The Noise Figure Calculator is built on the fundamental definitions from RF and communications system theory.
Noise Factor and Noise Figure
F = SNR_in / SNR_out
NF = 10 × log₁₀(F) [dB]| F (linear) | NF (dB) |
|---|---|
| 1.0 | 0 dB (ideal, noiseless) |
| 1.26 | 1 dB |
| 1.58 | 2 dB |
| 2.0 | 3 dB |
| 3.16 | 5 dB |
| 10 | 10 dB |
A system with NF = 3 dB has an output SNR exactly 3 dB worse than the input SNR — the system has doubled the noise power.
dB to Linear Conversion
F_linear = 10^(NF_dB / 10)
NF_dB = 10 × log₁₀(F_linear)The Noise Figure Calculator automatically converts between dB and linear values so you can enter data in whichever form is more convenient.
Friis Cascade Formula
For a chain of amplifiers or other two-port networks in series:
F_total = F1 + (F2 − 1)/G1 + (F3 − 1)/(G1 × G2) + (F4 − 1)/(G1 × G2 × G3) + ...where G_i is the linear power gain of stage i, and F_i is the linear noise factor of stage i.
Key insight: Each subsequent stage’s noise contribution is divided by the cumulative gain of all prior stages. This means:
- A high first-stage gain G1 suppresses the noise from all later stages.
- A high first-stage noise factor F1 directly adds to the total with no attenuation.
- This is why Low Noise Amplifiers (LNAs) with low NF and reasonable gain are placed first in RF receive chains.
Noise Temperature (Reference)
An alternative representation is the noise temperature T_e:
T_e = (F − 1) × T0where T_0 = 290 K (standard reference temperature). For example, NF = 1 dB (F ≈ 1.259) gives T_e ≈ 75 K.
Use Cases for Noise Figure Calculator
The Noise Figure Calculator is essential for RF, communications, and microwave engineering work:
- RF Receiver Design: Calculate the overall system NF of a receive chain including the LNA, filter, mixer, and IF amplifier. Use the Friis calculator to optimize the order and gain distribution of stages.
- LNA Evaluation: Enter the input and output SNR values measured from an LNA test bench to extract the device’s noise figure and compare against the datasheet specification.
- Link Budget Analysis: Incorporate the system noise figure into a link budget to determine the minimum detectable signal level and achievable receiver sensitivity.
- Cascaded Filter Loss: Passive components such as band-pass filters have a noise figure equal to their insertion loss in dB. Include filter stages in the Friis chain to see how loss degrades the total system NF.
- Education and Teaching: The Noise Figure Calculator provides a transparent Friis formula breakdown, making it ideal for RF systems courses, textbook examples, and lab report analysis.
- Satellite and Radar Systems: Evaluate the noise performance of low-temperature receivers and compare different system architectures to achieve the lowest possible noise floor.