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Insertion Loss question

Question asked by TDawe on Apr 14, 2009
Latest reply on Apr 15, 2009 by TDawe
I recently performed a bunch of tests on components - specifically variable attenuators, and they were all failing on our 40 MHz peak-to-peak specification over the X-band uplink and downlink frequency band.  Our specification is set for +/-.2dB over any 40 MHz band.  This is typical of my findings (all cables and connectors calibrated in the cal loop):

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When I complained to the vendor, he suggested I pad the input and output to the variable attenuator and try again.  I added a 6dB pad attenuator to the input and 3dB pad attenuator to the output, making sure it was calibrated in the cal loop first, ran only the most offending attenuator settings, and got this result:

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Can someone please explain to me how adding pad attenuators at the input and output of this variable attenuator changed the peak-to-peak measurements?  

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