Re: Spaced Coil measurements.

• To: tesla-at-pupman-dot-com
• Subject: Re: Spaced Coil measurements.
• From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Tue, 08 Jun 1999 06:06:12 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Ed,

> Original Poster: Ed Phillips <evp-at-pacbell-dot-net> 
> 
> "
> Hi Malcolm, All,
>     Using your measurements I get 18.25 pF from Medhurst's formula.  I
> plotted your data in Excel as 1/(f^2) VS C according to Howe.  A
> linear trend line fit to the data crosses the axis at about -50 pF.
> 50 pF seems a bit high.  You gave Ns = 38 turns for the whole coil?"
> 
>     My calculations agree almost exactly with Malcom's.  I have always
> found very good agreement (typically better than 5%) betweem the
> measured and calculated SRF's.  Do you have extra long leads, and do you
> really know the capacitance of your test capacitor?
> 
> Ed

Indeed! The first thing I did was to run for cover of the LCR 
analyser to check the caps which is why the E12 numbers have been 
given an extra significant digit. I suspected they were pretty close 
once I saw the initial inductance figures coming out of the mix. The 
leads were only just long enough for me to obtain the readings and 
the top lead goes straight back down the coil to the cap at the 
bottom. The relatively large shunt capacitances appear to swamp the 
small self capacitance of the lead which is what I was after. More 
checking with even greater spacing this weekend.

Cheers,
Malcolm

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