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mechanical vs solid state switching in the S param test set

Question asked by RadioRon on Oct 3, 2012
Latest reply on Oct 4, 2012 by Spacecase69
I'm not clear on what is happening in my NA.  It is an 8753E opt 11 using 87050A-H47 S parameter test set ( a close relative of the 85047A).   This test set has the mechanical switch in it, and I have gotten into the habit of pressing MEAS to update my measurement after a change.  I don't quite understand exactly why I need to do this.    For example, let's say I'm measuring input impedance to an amplifier using port 1.  I select S11 measurement type and Smith format and it looks smooth to start with.  Then I realize I have forgotten to terminate the output of this amplifier, so I attach port 2 to the output.  The S11 locus then changes as I expect but has become quite lumpy with little swirls in it.  Then I press MEAS, the test set relay clicks twice and now the S11 is nice and smooth, all lumps are gone.  What exactly has the analyzer done after I pressed the MEAS button versus before I did so?    

This becomes a problem when I want to check the effect of a change to the circuit but both of my hands are tied up and I can't press MEAS.  This is especially true when I'm tuning with a continuously variable component and want to see the change on the analyzer screen without having the press MEAS frequently.  Can I resolve this issue by installing a solid state switch?  Is there anything special about the switch retrofit kit other than the switch itself?  For example, how does the analyzer know if it has a mechanical or SS switch installed?

Edited by: RadioRon on Oct 4, 2012 1:03 PM  

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