Spectrum Analyzer units of measure
Converting from dBm/Hz to V/√Hz
Written by Paul Cracknell
Updated at February 26th, 2021
-
Moku:Go
Moku:Go Arbitrary Waveform Generator Moku:Go Data Logger Moku:Go Frequency Response Analyzer Moku:Go Logic Analyzer & Pattern Generator Moku:Go Oscilloscope & Voltmeter Moku:Go PID Controller Moku:Go Spectrum Analyzer Moku:Go Waveform Generator Moku:Go Power Supplies Moku:Go Digital Filter Box Moku:Go FIR Filter Builder Moku:Go Lock-in Amplifier
- Moku:Lab
- Moku:Pro
The Moku:Lab Spectrum Analyzer can display the spectrum amplitude in various units (dBm, Vrms, Vpp and dBV). Additionally, you can select corresponding power spectral density (PSD) units (dBm/Hz, Vrms/√ Hz, Vpp/√Hz and dBV/√ Hz). It is worth noting that the Resolution Band Width (RBW) setting only affects the measurement in PSD units.
Below is an example from the Moku:Lab demo mode, the channel 1 peak is shown at -73.75 dBm/Hz.
This can be converted to Vrms/√Hz by relationship P [mW/Hz] = 10^ (P [dBm/Hz] / 10)
So in this case, P = 4.22 x 10 -8 mW/Hz
Also, V= √( P x R) and that here 50 ohms is the conventional nominal impedance.
Thus the spectral peak in volts, allowing for conversion from mW to W, is
V = √( 50 x 4.22 x 10 -11)
V = 45.9 μV/√Hz
In this second screenshot of the Moku:Lab Spectrum Analyzer demo mode, the units have been switch to uV/√Hz.
