Noise Figure & Receiver Sensitivity
Calculate receiver sensitivity from noise figure and bandwidth, or compute cascaded system NF using the Friis formula.
IEEE/3GPP standard: 290 K. Lower for satellite/cooled receivers.
| Thermal noise floor | -100.96 dBm | −174 + 10·log₁₀(2.00e+7) |
| Noise floor + NF | -95.96 dBm | -100.96 + 5 dB |
| Receiver sensitivity | -85.96 dBm | N_floor + NF + SNR_min |
Key Formulas
Thermal noise floor
N (dBm) = −174 + 10·log₁₀(BW_Hz) [at T = 290 K]
Receiver sensitivity
S_min = N + NF + SNR_min
Friis cascaded noise factor (linear)
F_total = F1 + (F2−1)/G1 + (F3−1)/(G1·G2) + …
Convert dB ↔ linear
F = 10^(NF_dB / 10)
G = 10^(Gain_dB / 10)
Typical Noise Figure Values
Understanding where noise is introduced helps prioritise improvements. The LNA at the antenna input is the most critical element — any noise it adds is amplified through the rest of the chain. For link budget calculations using these sensitivity values, see the link budget calculator. To compare calculated sensitivity against measured signal, use RSRP / RSRQ. PIM products are another key noise source that can raise the effective noise floor above the thermal limit.
| Component | Typical NF | Notes |
|---|---|---|
| LNA (low noise amp) | 0.5–3 dB | First stage — most critical |
| Bandpass filter | = insertion loss | Passive: NF = loss |
| Cable/connector | = insertion loss | Passive: NF = loss |
| Mixer (passive) | 5–10 dB | Conversion loss dominates |
| ADC + front-end | 10–20 dB | System NF after LNA |
| Typical LTE eNB | 5 dB | 3GPP TS 36.104 reference |
| Typical NR gNB | 5 dB | 3GPP TS 38.104 reference |
Frequently Asked Questions
What is noise figure and why does it matter?▾
Noise figure (NF) is a measure of how much noise a device adds to the signal passing through it, expressed in decibels. An ideal noiseless amplifier has NF = 0 dB. The NF of the first stage in a receiver chain (typically an LNA — Low Noise Amplifier) dominates the overall system noise because any noise added early is amplified by all subsequent stages. A 1 dB improvement in the LNA noise figure improves receiver sensitivity by 1 dB, directly extending cell coverage range.
How is receiver sensitivity calculated?▾
Receiver sensitivity is the minimum signal power a receiver can detect reliably at a given error rate. It equals the thermal noise floor plus the system noise figure plus the required minimum SNR: S_min = −174 dBm/Hz + 10·log₁₀(BW_Hz) + NF + SNR_min. For a 20 MHz LTE receiver (NF = 7 dB, SNR_min = −1 dB for QPSK): S_min = −174 + 73 + 7 − 1 = −95 dBm.
What is the Friis noise figure formula?▾
The Friis formula calculates the total noise figure of a cascaded chain: NF_total = F1 + (F2−1)/G1 + (F3−1)/(G1·G2) + … where F = 10^(NF_dB/10) and G = 10^(Gain_dB/10) are linear values. The key insight is that the first stage contributes its full NF to the system, while later stages contribute less because earlier gain reduces their relative noise contribution. This is why high-gain, low-NF LNAs are placed first in receiver chains.
What is the standard noise temperature used in calculations?▾
The IEEE and 3GPP standard reference temperature is T₀ = 290 K (17°C), which gives a thermal noise density of −174 dBm/Hz (kT₀ = 4.002×10⁻²¹ W/Hz). At this temperature, a 20 MHz bandwidth has a noise power of −174 + 73 = −101 dBm. Satellite receivers sometimes use lower effective temperatures (50–200 K) to account for the cold sky; terrestrial cellular receivers use 290 K as the standard.