Compute noise figure, factor, and temperature for amplifiers. Use SNR data, noise factor, temperature, or Friis stages. Export results with clear units always included.
Noise factor: the ratio of input to output SNR.
Noise figure (dB): logarithmic form of noise factor.
Equivalent noise temperature: relates F to a reference temperature.
Friis cascade equation: total noise factor for stages with gains G.
| Scenario | Inputs | Output | Meaning |
|---|---|---|---|
| Measured SNR drop | SNR in 50, SNR out 20 | NF ≈ 3.98 dB | Amplifier reduces SNR by 2.5×. |
| Known noise factor | F = 2.0 | NF ≈ 3.01 dB | Common low-noise front-end value. |
| Noise temperature model | Te = 290 K, T0 = 290 K | NF ≈ 3.01 dB | Te equals T0 gives F = 2. |
| Three-stage cascade | G: 20/10/8 dB, NF: 2/4/6 dB | NF ≈ 2.63 dB | High first-stage gain protects later noise. |
Noise figure quantifies how much an amplifier degrades signal‑to‑noise ratio. A 0 dB figure is ideal, while 3 dB means the output SNR is halved. Each added dB reduces sensitivity and link margin for weak signals.
This calculator links noise factor F (linear), noise figure in dB, and equivalent input noise temperature Te. With the common reference T0 = 290 K, Te = 290 K gives F = 2 and NF ≈ 3.01 dB, matching many datasheets. Te is handy for antenna temperature and cryogenic work, where temperatures add more naturally than decibels.
Friis’ equation shows the first stage noise factor appears without attenuation, while later stages are divided by preceding linear gain. A low‑noise front end with 20 dB gain (×100) can suppress the next stage’s contribution by about 100×.
RF front ends often target about 0.5–2.5 dB depending on frequency and device technology, while general gain blocks may land around 4–8 dB. IF and audio designs may specify voltage noise instead, but SNR degradation is the same story.
Thermal noise density at 290 K is about −174 dBm/Hz. An NF of 3 dB raises the effective input noise density to roughly −171 dBm/Hz. Over bandwidth B, total noise rises by 10·log10(B), so wideband receivers pay a real penalty.
If you measure SNR at the amplifier input and output using the same bandwidth and detector settings, the ratio gives F directly. Keep the setup stable, avoid clipping, and ensure the output measurement includes the amplifier’s added noise, not extra processing gain.
Gains and noise figures are entered in dB for convenience, but Friis requires linear gain and linear noise factors. The calculator converts internally and reports total NF plus each stage’s contribution term, helping you decide whether better first‑stage NF or more gain matters most.
Verify units, confirm SNRout is lower than SNRin, and compare results to realistic ranges for your band. Exporting CSV or PDF supports design reviews and test logs during early architecture studies. Even a 1 dB improvement can translate into meaningful range or throughput gains.
1) What is the difference between noise factor and noise figure?
Noise factor (F) is a linear ratio of SNRin to SNRout. Noise figure is the same quantity expressed in decibels: NF(dB) = 10·log10(F).
2) Why is 290 K used as the reference temperature?
290 K is a widely adopted industry reference for comparing devices. It approximates room temperature and ties noise temperature to the −174 dBm/Hz thermal noise density baseline.
3) Can an amplifier have a noise figure below 0 dB?
For passive, linear devices referenced to 290 K, NF is typically ≥ 0 dB. Apparent sub‑0 dB results usually indicate measurement or calibration issues, or a different reference definition.
4) How does bandwidth affect noise figure calculations?
Noise figure itself is a ratio and does not depend on bandwidth if measured consistently. However, total noise power grows with bandwidth, so system noise floor and sensitivity strongly depend on B.
5) Why does high first‑stage gain help overall noise figure?
Friis’ equation divides later stage noise contributions by the preceding linear gain. A strong, low‑noise first stage reduces how much downstream stages can degrade the overall chain.
6) What inputs should I use for the SNR method?
Use linear SNR values measured with the same bandwidth, detector, and averaging settings at input and output. If you have SNR in dB, convert to linear before entering.
7) When should I use the cascade mode instead of single‑stage?
Use cascade mode when multiple components contribute to the receiver front end, such as LNA, filter, mixer, and IF amplifier. It helps identify which stage dominates the total noise performance.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.