Receiver Noise Floor

Formula

Description

The noise floor of a receiver is the minimum detectable signal level, determined by thermal noise, the receiver noise figure, and the bandwidth. The −174 dBm/Hz is the thermal noise power spectral density at room temperature (290 K): kTB in dBm with B = 1 Hz. The noise figure NF adds the receiver internal noise contribution. Wider bandwidth captures more noise power. This formula is fundamental to receiver sensitivity analysis, link budget calculations, and dynamic range assessment in RF, radar, and communication systems.

Variables

• Noise Floor — Minimum noise power in the receiver (dBm)
• NF — Receiver noise figure (dB)
• BW — Receiver bandwidth (Hz)

Practical Notes

Example: An LNA with NF = 2 dB and 200 kHz bandwidth has a noise floor of −174 + 2 + 10×log₁₀(200000) = −174 + 2 + 53 = −119 dBm. The receiver sensitivity is the noise floor plus the minimum required SNR for demodulation. For narrowband systems (LoRa, CW), the narrow bandwidth lowers the noise floor significantly, enabling long-range communication.