Download STANFORD RESEARCH SYSTEMS SR760 User

MEASURE MENU
Measure
The Measure sub menu selects the type of measurement for the active trace.
Spectrum
The SR760 filters the input data in real time to provide a time record with the
desired frequency span and then performs an FFT on this record. Pressing
the Spectrum key displays this FFT on the active trace.
PSD
The PSD or Power Spectral Density is the magnitude of the spectrum (the
square root of [the FFT times its complex conjugate]) normalized to a
bandwidth of 1 Hz. This measurement approximates the amplitude within a 1
Hz bandwidth located at each frequency bin. The actual linewidth and
window function are compensated for in this calculation. This allows
measurements taken with different spans or windows to be compared.
Note:
PSD measurements are typically used to measure noise or noise density.
The data values are read out in Volts/√Hz or dBV/√Hz. When measuring
Gaussian noise sources, the noise in bandwidths other than 1 Hz may be
obtained by multiplying the reading by the square root of the desired
bandwidth. This is true only for Gaussian noise.
When measuring PSD, the Display may only be set to Log Magnitude or
Linear Magnitude.
4-4