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Local Oscillator Feedthrough

Question asked by SOLT_guy on Jul 31, 2012
Latest reply on Sep 13, 2012 by SOLT_guy
Dear Sir:

      I was reading Agilent application note 150, entitled, "Spectrum Analysis."

     I have uploaded a copy of this application note for your convenience.

      Page 8 of the application note states:

      "When the local oscillator equals the IF, the local oscillator signal itself is processed by the system and appears as a response in the display...L.O. feedthrough actually can be used as a 0 Hz marker."

      I have viewed Agilent tutorials with regard to this condition and a question always arises whenever I see this teaching model (the model seeks the viewer to observe the difference frequency).   We see a constant LO frequency but, I am led to believe that the LO signal is a swept signal.   I would surmise that, in reality, the LO signal would be sweeping so fast that we would not be able to see the frequency sweep.

       Why was the signal data processed in this manner?

Edited by: SOLT_guy on Oct 5, 2012 8:38 AM