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High Frequency Oscilloscope Measurements

Question asked by SOLT_guy on Mar 11, 2013
Latest reply on Mar 13, 2013 by algoss
Dear Sir:

       I was wondering if you could tell me how Agilent makes accurate voltage measurements at high frequency.  

       Consider this question:

        Generally, oscilloscopes make measurements with an internal impedance of 1 Megaohm or 50 ohms.    I read that, in the past, that when an oscilloscope made a measurement when the internal impedance was set to 50 ohms, that 50 ohm resistance would be in placed parallel with the load.   This is equivalent to using a 50 ohm feedthrough when scopes were fixed at a 1 Mega ohm input impedance.   It follows logically, if one were measuring a the voltage across an external 50 ohm resistance, the equivalent resistance would be approximately 25 ohms.    (I realize, the method I have just described is simplistic and cannot be practically applied after giving this some more thought).     This would indicate, at this setting that one would measure the a voltage drop across a 25 ohm resistance.   Can you tell me how this issue is resolved?   Does Agilent use a correction factor (data processing) to obtain the correct result?

        Next question:

        When oscilloscopes make measurements at high frequencies, (Agilent has advertised a raw measurement bandwidth at its pre-amps at approximately 26 GHz),  there are SWR issues that take place at the measurement point.    Can you tell me how Agilent resolves this issue?

Edited by: SOLT_guy on Mar 11, 2013 10:43 AM