Spectral mask and power spectral density

1. What is a power spectral mask?
2. How is spectral power density measured?

What is a power spectral mask?

A Spectral Mask makes sure a transmission stays within its band and, therefore, reduces interference by limiting excessive radiation at frequencies beyond the necessary bandwidth.

How is spectral power density measured?

Answer. PSD is typically measured in units of V_rms² /Hz or V_rms/rt Hz , where "rt Hz" means "square root Hertz". Alternatively, PSD can be expressed in units of dBm/Hz. On a spectrum analyzer such as the PSA, ESA, 856XE/EC or 859XE, power spectral density can be measured with the noise marker.