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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 measurementsâ€¦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 â€œSignal Separation Chartâ€ to find the â€œEffective Return Lossâ€.  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 â€œEffective Return Lossâ€ of the sliding load? ......Should I be able to re-measure the sliding load if I just used it to cal up my system?