dear all
      i need your help,here is my question:i want to use PXF analysis of spectreRF simulator to evaluate the power noise effect on the phase noise of VCO output.but i cannot get the waveform.
      my PSS setting is like this:
.beat freq=400M    //VCO output 426M
.number of harmonics =10  
.accuracy default: moderate
.tstab=200n
.hlight oscillator  and choose OSC node and reference node
  my PXF setting is like this:
.sweeptype=relative and relative harmonic=1
.sweep range:1K to 250M
.points per decade =10
.maximum sideband=1
.select positive output node and negative output node
.choose modulated for specialized analysis
.outputtype=SSB/AM/PM
.input modulated harmonic list=1 0
.output modulated harmonic =1
      after the simulation,i select the direct plot form,and click "pxf modulated",choose SSB for input,PM for output;0 0 for modulated input harmonic and 426.903M 1 for modulated output harmonic.
  however,after i selected the power voltage source.simulator told me :
*error* mag: can't handle mag(nil)
*error* evaluating expression (_drplModPxfVGain('SSB 0 'PM 1 '("/V0" "/VDDA/" "/gnd!")))
*error* ("difference" 0 t nil ("*error* difference:can't handle (nil - 0.0)"))

Which subversion of Virtuoso are you using (Help->About in the CIW), and which subversion of spectre (this will appear at the top of the spectre output log).

I was using IC615 ISR17 and MMSIM131 ISR2 - and I followed the steps you are doing and was able to plot the waveforms OK from the direct plot form.

Regards,

Andrew.