Lambda SR1, Operation Manual, Page: 181 / 317

SR1 Operation 181
© 2014 Stanford Research Systems
Resolution and Bandwidth
The number of lines in the jitter FFT can be set from 256 to 32k lines using the "Resolution control".
These lines span the frequency range from DC to the value set in the "Bandwidth" control. The ADC
used by the jitter detector, like all of SR1's converters is preceded by an anti-aliasing filter with a finite
attenuation slope. As a result, some lines at the upper edge of the frequency range may not be
protected against aliases to the full attenuation of the filter. If "Show Aliased Lines" is checked, SR1 will
display the entire spectrum up to Fs/2 including lines that may not be fully alias-protected. If the control
is unchecked only fully alias-protected lines will be displayed and the bandwidths will be adjusted
accordingly.
Total Jitter
The RMS Sum control displays the "total" jitter found by RMS summing all the points in the jitter FFT. It
will, in general, agree with the "Reading" calculated by the Time Domain jitter analyzer. The sum is
performed after all filtering and weighting is applied.
Filtering
Adjustable highpass, lowpass, and weighting filters can be applied to the jitter spectra and the RMS
sum calculation . These filters are applied by the DSP after the jitter FFT has been computed. The
highpass and lowpass filters are 4th order Butterworth filters. Each filter is enabled or disabled by the
corresponding checkbox. The weighting filter choices are same as for the
Time Domain Detector . See
the discussion there for the types and intended applications of each of the weighting filters.
Averaging