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Are IQ samples missed while capturing the data?

Hi Aaronia team,

I am trying to demodulate a 5 MHz signal which is captured from the Spectran V6 using simple IQ recorder mode. (reference: I have put time to frequency converter block and observing spectrum plot for just for confirming (find the attached mission file).

These are the Spectrn Pro status: Only  Rx1 is ON with full span. No USB underrun/overrun observed. Ensured that the DSP load and CPU load doesn't cross 70%.

Here are my observations:

  1. The spectrum outside the 5MHz band jumps every now and then (observed in the IQ power spectrum).
  2. When the signal is plotted in the spectrogram of Matlab (plot using spectrum analyzer), there are spurs at various time points.
  3. When the signal is read back ( I avoided using spectrogram in this mission to save resources on the CPU) using file reader, the energy  outside the 5MHz BW is visible.
  4. The signal from the generator is clean as seen with competitor signal analyzer.


  1. Mission file
  2. IQ capture spectrum  screenshot (video is sent over email).
  3. Matlab spectrogram plot
  4. Aaronia spectrogram plot using file reader.
  5.  Competitor Spectrum Analyzer plot to show the signal do not have issue .

Kindly help me here, on what is going wrong.


Uploaded files:

Looks like PC limitations!

Lower the bandwidth (data amount) e.g. use a SPAN of 1/2 or 1/4 and remove the IQ Power Spectrum block.

Do you then get a clean recording?

Reducing the span to 1/2 and 1/4 made it to work.

IQ power spectrum block was used turned off anyway.