dBm per Hz (dBm/Hz) also called Power Spectral Density, is the amount of power in dBm per Hertz of bandwidth.
To convert dBm/Hz to dBm, enter the power value and desired bandwidth in the calculator below.
The tool will calculate the power over this bandwidth and provide a value in both dBm and Watt.
dBm to dBm/HzWhat is dBm/Hz used for?
dBm/Hz is the power of the signal measured in a 1 Hz resolution bandwidth. The measurement of signal power is normalized to 1 Hz.
This unit is often used to specify the sensitivity of a spectrum analyzer. Manufacturer’s call it the Displayed Average Noise Level (DANL).
The lower the DANL, the more sensitive the analyzer. The lowest noise floor that can be theoretically measured at 0oC is -174 dBm/Hz. This assumes a noise figure of 0 dB.
As the Resolution Bandwidth (RBW) setting of the analyzer is increased, the DANL increases and this tool can be used to calculate that level.
*Most modern spectrum analyzers calculate a Fast Fourier Transform on the input sampled RF signal. Use this tool to understand how the RBW is calculated from the Span setting and FFT size.
Example Calculation
What does a PSD value of -174 dBm/Hz equate to over a 100 kHz bandwidth?
Assuming the PSD is constant over the bandwidth (100 kHz = 100000 Hz), the calculator can be used to find the answer is -124 dBm.
To do this manually, the formula for the integrated power is:
-174 + 10*Log10(100000) = -174 + 50 = -124 dBm
The wider the integration bandwidth, the higher the total power level. This assumes the signal spans the bandwidth under consideration.
The dBm to Watt converter is used to compute the equivalent 3.981e-16 Watt.
Notes
[1] Use this calculator to convert between user-defined values of RBW. For instance to convert from -95 dBm at 1 kHz RBW to 100 MHz RBW.
[2] Power Spectral Density on Wikipedia