Noise Figure & Noise Temperature Calculator
Convert RF noise figure, noise factor, equivalent noise temperature, thermal noise, noise floor and cascaded receiver noise figure using the standard Friis noise formula.
RF-011 focuses on receiver noise calculations. It does not calculate receiver sensitivity, complete link budgets, phase noise, oscillator noise or ADC SNR.
Engineering tool
Noise Figure & Noise Temperature Calculator
Convert RF noise figure, noise factor, equivalent noise temperature, thermal noise, noise floor and cascaded receiver noise figure.
Result console
- Noise Figure
- 3dB
- Noise Factor
- 1.99526231
- Equivalent Noise Temperature
- 288.626071 K
- Bandwidth
- Not required
- Physical Temperature
- 290 K
- Thermal Noise
- Not required
- Thermal Noise dBm
- Not required
- Noise Floor
- Not required
- Cascaded Noise Figure
- Not required
- Formula Used
- F = 10^(NF / 10)
Noise figure is not the same as SNR. It describes how much a device or chain degrades signal-to-noise ratio.
Formula reference
Noise Figure and Thermal Noise Formulas
Noise figure uses logarithmic dB values, but Friis cascade calculations must use linear noise factors and linear gains internally.
F = 10^(NF / 10)NF = 10log10(F)Te = 290 × (F - 1)NF = 10log10(1 + Te / 290)P = kTBNoise Floor(dBm) = 10log10(kTB / 1 mW) + NFFtotal = F1 + (F2 - 1)/G1 + (F3 - 1)/(G1 × G2) + ...Variable definitions
- NF
- noise figure in dB
- F
- linear noise factor
- Te
- equivalent input noise temperature in kelvin
- 290 K
- standard reference temperature
- k
- Boltzmann constant, 1.380649 × 10^-23 J/K
- T
- physical temperature in kelvin
- B
- noise bandwidth in hertz
- G
- stage gain converted to a linear power gain
Worked Examples
3 dB noise figure
F = 10^(3/10) = 1.995, so equivalent noise temperature is about 288.6 K.
290 K noise temperature
F = 1 + 290 / 290 = 2, so NF = 10log10(2) = 3.01 dB.
1 MHz thermal noise
At 290 K, P = kTB gives about -113.98 dBm in 1 MHz.
10 MHz noise floor
At 290 K and NF = 3 dB, noise floor is about -100.98 dBm.
LNA 1 dB, 20 dB gain plus mixer 6 dB
Friis formula gives cascaded NF about 1.10 dB because the high-gain LNA suppresses mixer noise contribution.
Three-stage receiver chain
A low-noise first stage with useful gain usually matters more than improving a later IF stage by the same noise-figure amount.
100 kHz bandwidth
At 290 K, 100 kHz thermal noise is about -123.98 dBm before receiver noise figure is added.
Compare two LNAs
A 0.8 dB LNA with 18 dB gain usually produces a lower cascaded NF than a 2.2 dB LNA with 12 dB gain before the same mixer.
0 dB noise figure
F = 1 and Te = 0 K, representing an ideal noiseless device, not a practical RF component.
6 dB noise figure
F = 3.981, so the equivalent input noise temperature is about 864 K.
Engineering Notes
- Lower noise figure is better for weak-signal receiver performance.
- Bandwidth directly raises noise floor through the 10log10(B) term.
- 290 K is the standard reference temperature for noise figure and equivalent noise temperature.
- Friis noise formula makes the first LNA especially important.
- Gain entered in dB must be converted to linear gain before Friis cascade calculation.
- Noise figure is not SNR; it describes SNR degradation.
- Thermal noise is also called Johnson noise.
- Noise floor combines thermal noise, bandwidth, physical temperature and receiver noise figure.
- Loss before the first LNA directly hurts receiver noise performance.
- Use measured device noise data and real filter bandwidth for production receiver design.
Common Mistakes
- Treating noise figure as noise floor.
- Putting dB gain directly into the Friis formula instead of converting to linear gain.
- Ignoring receiver bandwidth.
- Assuming temperature is always exactly 290 K.
- Ignoring filter or cable loss before the first LNA.
- Comparing two receivers without using the same bandwidth.
- Confusing noise factor with noise figure.
- Using ideal thermal noise as a complete receiver sensitivity calculation.
Support reference
FAQ
What is noise figure?
Noise figure is the amount by which an RF device or receiver chain degrades signal-to-noise ratio compared with an ideal noiseless device.
How do I calculate noise temperature?
Convert noise figure to noise factor with F = 10^(NF/10), then calculate equivalent noise temperature with Te = 290 × (F - 1).
What is thermal noise?
Thermal noise is random Johnson noise caused by temperature. For an ideal resistor or matched source, available noise power is P = kTB.
Why is -174 dBm/Hz important?
-174 dBm/Hz is the common 290 K thermal noise density approximation for a 1 Hz bandwidth. It is a reference starting point for RF noise-floor estimates.
How does bandwidth affect noise floor?
Noise floor rises with bandwidth according to 10log10(B). Increasing bandwidth by 10 times raises the noise floor by 10 dB.
Why is the first LNA critical?
Friis noise formula shows that later-stage noise is divided by the gain of earlier stages. A low-noise, high-gain first stage usually dominates receiver noise performance.
What is Friis noise formula?
Friis noise formula calculates cascaded noise factor as Ftotal = F1 + (F2 - 1)/G1 + (F3 - 1)/(G1 × G2) + ... using linear noise factors and linear gains.
How do I reduce receiver noise?
Use a low-noise first amplifier, place it close to the antenna, minimize pre-LNA loss, use appropriate bandwidth and verify noise performance with real device data.
Is noise figure the same as noise floor?
No. Noise figure is a device or chain property. Noise floor depends on thermal noise, bandwidth, temperature and receiver noise figure.
Can this calculator predict receiver sensitivity?
No. Receiver sensitivity also depends on required SNR, modulation, coding, bandwidth, implementation loss and detection criteria.
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Future Engineering Guide Topics
Noise Figure Explained
In_DevelopmentNoise Temperature
In_DevelopmentFriis Noise Formula
In_DevelopmentThermal Noise
In_DevelopmentReceiver Design
In_DevelopmentDisclaimer
This calculator provides RF noise estimates using standard ideal formulas. Final receiver designs should be verified with device datasheets, measured bandwidth, gain compression, impedance matching and system-level sensitivity requirements.