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VNA measurements and TDR gating

Question asked by SOLT_guy on Aug 19, 2012
Latest reply on Aug 27, 2012 by Dr_joel
Dear Sir:

      I need to measure a load accurately for a one port measurement.   The problem is there are other devices interposed between my load and port 1 of my VNA such as adapters, fixturing connectors, etc..   I would like to use the NA's TDR function as a means to set gate start and stop times so that I may measure only my load in isolation.   

      Generally, the method to make this type is measurement is to set the gate start and stop times and then disable the transform function (although gating is enabled)  and then view the load on a Smith Chart.

       My question is this, in order to mark the best start and stop times using the gating function, what TDR function is best to use to "mark" the gate start and stop time.   

        I like to use the the impulse response function to mark the start gate time.  I generally set the start time at the peak of the impulse response when I am certain I have detected the physical position of the load.    Can you tell me, for the most accurate measurement measurement of my load should I set the start time at the base of the impulse response at the load point (the base point I am referring to marks the beginning of the upward slope of the impulse signal) or at the peak of the impulse response?    Keep in mind the measurement I am making does not use the impulse response to make the measurement of the load itself, the impulse response is only used to mark the start gate time before I disable the TDR option (but gating is enabled).

        To determine the optimum stop gate time to capture data referenced to only the load is the primary reason why I have written this post, can you tell me how I should go about determining the best gate stop time to make the most accurate measurement of my load?

Edited by: SOLT_guy on Aug 19, 2012 8:23 PM