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Re: Using the MFJ269 to measure inductance.

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  • hopperdhh@aol.com
    Hi all, I don t think that measurement error is what you should be concerned with. The MFJ can measure the inductors with good enough accuracy. Yes, you do
    Message 1 of 6 , Dec 3, 2009
       
      Hi all,
       
      I don't think that measurement error is what you should be concerned with.  The MFJ can measure the inductors with good enough accuracy.  Yes, you do need to be aware of the accuracy of your test equipment, but more important in this case is the fact that the filters are broad and it isn't necessary to use exact values.
       
      I asked a similar question a few weeks ago about capacitor values, and got similar answers that said basically just build it and don't worry about it!
       
      What I did to satisfy my curiosity was to use LTSpice to model the filter.  The LTSpice schematics of the filters can be found in the Files.  I duplicated the filter schematic except for the source voltage and then changed the capacitor that I was concerned with to the value I measured.  That is, I had two similar filters driven from the same source voltage so I could display the two responses at once.  One had ideal values for L and C as a reference (I calculated the series resistance of the coils for a Q of 200 at the mid band frequency), and in the other filter I played with values to see what difference it made in the response.
       
      In my case I was worried about a capacitor that was 10 or 15 percent high, but the same test could be applied to inductors.
       
      Long story short, there is very little difference in the overall response caused by varying the values over quite a large range.
       
      I love LTSpice!  Its free, easy to use, and quite useful.
       
      Dan K9WEK
       
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