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Sliding Loads...are they magical?

Question asked by Sterling019 on Feb 9, 2007
Latest reply on Feb 16, 2007 by daveb
What is the theory behind using a sliding load to perform the cal on a VNA.  I know that it changes the phase and somehow yields for greater return loss measurements…but why and how??  Out of the six set points (such as the sliding load in the 85052B kits), what would be the results if I only used four of the set points??  What would the results be if I also performed a set in between each detent making eleven or twelve set points?

     Is there a way that I can test my system after a calibration to make sure that it is capable of measuring devices with a return loss of 40dB or greater?  If I connect the sliding load back up to the VNA after a calibration then it shows a return loss of 30 to 35 dB although the sliding load has a return loss spec. of 44dB. --When I test the directivity of bridges with very low return loss, we move the sliding load back and forth to find the max. and min. return loss values of a particular frequency of interest.  We then use a “Signal Separation Chart” to find the “Effective Return Loss”.  Is this method the same if I wanted to measure the return loss of the sliding load to verify the cal of the 8510C or any VNA at higher frequencies?  Is there a formula to calculate the “Effective Return Loss” of the sliding load? ......Should I be able to re-measure the sliding load if I just used it to cal up my system?