Power measurements are usually made with a user-specified bandwidth. This tool converts this power reading to a normalized value of 1 Hz bandwidth.
dBm per Hz (dBm/Hz) also called Power Spectral Density, is the amount of power in dBm per Hertz of bandwidth.
To convert dBm to dBm/Hz, enter the value and the bandwidth in the calculator below.
Formula
PdBm/Hz = PdBm – 10*Log10(B)
where, PdBm is the power measured in Bandwidth B
Applications of this calculator
Compare Spectrum Analyzer Noise Floor
Many spectrum analyzer manufacturers use different bandwidth settings to specify their noise floor.
TinySA’s noise floor specifications state the lowest discernible signal using a resolution bandwidth of 30 kHz of -102 dBm. The calculator can be used to convert this to -147 dBm/Hz.
This can be compared with the noise floor of a Siglent Spectrum Analyzer which is more sensitive at -161 dBm/Hz. That’s a difference of 17 dB and this makes a benchtop analyzer about 50 times more sensitive than the Tiny SA.
Many times a manufacturer will omit the bandwidth specification when specifying the sensitivity of their instrument. As can be seen in the above examples, the bandwidth influences the number significantly.
Convert RBW settings
Let’s say you want to convert a measurement that was made in a 30 kHz resolution bandwidth to 1 MHz resolution bandwidth.
- Use the calculator on this page to normalize from dBm/ 30 kHz to dBm/Hz
- Then enter this number in this calculator along with the desired bandwidth of 1 MHz. This will convert from dBm/Hz to dBm/ 1 MHz
Notes
[1] Use this calculator to convert between user-defined values of RBW. For instance to convert from -110 dBm at 10 kHz RBW to 10 MHz RBW.