Spectrum Analyzer DANL & Sensitivity

The displayed average noise level (DANL) is a spectrum analyzer's own noise floor — the lowest signal it can show. It is the thermal noise in the resolution bandwidth plus the instrument's noise figure (which input attenuation adds to directly). Narrowing the RBW lowers the floor by 10 dB per decade; the smallest signal you can actually measure sits your required SNR above it.

Equations & Parameters ▸

\(\text{DANL} = -174\ \text{dBm/Hz} + NF + L_{\text{att}} + 10\log_{10}\text{RBW}\)
\(\text{sensitivity} = \text{DANL} + \text{SNR}_{\min}\)

RBW	Resolution bandwidth (Hz).
NF	Analyzer noise figure (dB) at 0 dB input attenuation.
L_att	Input attenuation (dB), optional — adds one-for-one to the noise floor.
SNR_min	SNR you need above the noise floor to measure a signal (dB), optional.
DANL	Displayed average noise level (dBm) in the chosen RBW.

References: Keysight, App. Note 150, Spectrum Analysis Basics. · Rohde & Schwarz, Fundamentals of Spectrum Analysis.

Inputs

Resolution BW, RBW

e.g. 1e3

Noise figure, NF

Analyzer NF

Input atten., L_att (optional)

Default 0

Required SNR (optional)

For sensitivity

Results

Noise floor

DANL—

Noise density—

Sensitivity

Min. signal—

DANL @ 1 Hz—

Diagram

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