Y Unit (Y Scale)
The parameter is located on the Y Scale tab for traces and in the Units tab of the for use with limit lines.
The y-axis units that can be selected depend on two things: the measurement calculation and the format used to display the data. Trace Data determines the measurement calculation; Trace Format determines the format the VSA uses to display the data.
Power units are valid only with these trace formats: , , and .
For some combinations of and , y-axis units cannot be selected because the y-axis is unitless. For other combinations, only one unit may be able to be selected or there may be several units to select from.
Most y-axis units are probably familiar. However, units used for Power Spectral Density (PSD Power Spectral Density: See power spectral density.) measurements may not be so familiar:
- dBm deciBels referenced to a milliWatt: dB relative to 1 milliwatt dissipated in the nominal input impedance of the analyzer/Hz (default units for PSD)
- Vpk/rtHz
- Vpk^2/Hz
Vpk/rtHz displays the trace in volts divided by the square root of equivalent filter bandwidth (this is the square root of the power spectral density). Other choices available may be Vrms/rtHz, dBVrms/rtHz, or dBVpk/rtHz.
Vpk^2/Hz displays the trace in volts squared divided by the equivalent filter bandwidth. This provides power normalized to a 1 Hz bandwidth or power spectral density (PSD). Other choices available may be Vrms^2/Hz.
Two other Y-axis units you may find useful are "mRMS" (milli-RMS), which is the same as RMS except for a factor of 1000, and "dBmVrms," which adds 60 dB to the dBVrms. These units are helpful when looking at very small signals.
