Re: Spaced Coil measurements.

• To: tesla-at-pupman-dot-com
• Subject: Re: Spaced Coil measurements.
• From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Wed, 02 Jun 1999 07:50:31 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Barry,

> Original Poster: "B**2" <bensonbd-at-erols-dot-com> 
> 
> 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?

Your value of Cself would be closer than mine. I guestimated a figure 
for Medhurst's H factor from the h/d ratio. The plot seems to suggest 
that something's not quite right with this coil. I'll double-check 
the turns but 38 is what I wound I'm sure. This gives around 1.1 TPI 
with relatively tiny Dwire.

I'm going to follow up on Terry's suggestions this weekend to get 
more data. The idea is to hold h/d constant (and hence Cself if 
Medhurst holds good) while progressively reducing turns to 1. I might 
not get to 1 as the frequencies will get beyond the range of my Lo Z 
signal generator rather quickly and I may have to resort to using a 
higher impedance (transformed perhaps) RF generator. There was no 
point in starting with a closewound coil. I think we all know the 
results of doing that ;)

Cheers,
Malcolm

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