RE: [TCML] Primary selfC

[G Hunter <dogbrain_39560@xxxxxxxxx>]

Years ago in a magazine advertisement for a compact HF ham radio antenna, I read that ribbon conductors are not so great for RF.  The advertiser claimed that RF currents tend to concentrate on the knife edges of the ribbon, rather that spreading out evenly on all that glorious surface area.  Of course, this manufacturer was using round metal tubing for his antenna, while his competitor was using metal ribbon!  Even so, that doesn't mean it isn't true.

If RF currents really do favor the edges of ribbon-shaped conductors, this would go far toward explaining the counter-intuitive results of your Cu ribbon AC resistance measurements.

Greg


--- On Sun, 7/27/08, Lau, Gary <Gary.Lau@xxxxxx> wrote:

> From: Lau, Gary <Gary.Lau@xxxxxx>
> Subject: RE: [TCML] Primary selfC
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Sunday, July 27, 2008, 10:10 AM
> I would agree that a spiral ribbon is not the best choice
> for a high-Q primary.  When I made AC resistance
> measurements on several different primary conductors, all
> of the same inductance, a 1" x .03" copper ribbon
> showed a slightly higher AC resistance than a coil of
> 1/4" Cu tubing, over all frequencies of interest,
> despite having less than half of the tubing's DC
> resistance.  I attributed this to eddy currents; not sure
> how this differs from proximity losses.
> 
> http://www.laushaus.com/tesla/primary_resistance.htm
> 
> Regards, Gary Lau
> 
> 
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx
> [mailto:tesla-bounces@xxxxxxxxxx] On
> > Behalf Of Paul Nicholson
> > Sent: Saturday, July 26, 2008 5:26 PM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] Primary selfC
> >
> > This compact ribbon primary is proving to be
> interesting. The
> > high turn-to-turn capacitance is turning out to have a
> > non-negligible contribution to the internal
> capacitance of
> > the coil, which as a result, affects the coil's
> effective
> > inductance and will lower the resonant frequency.  By
> how much?
> > I hope to be able to estimate this, or at least point
> the way.
> >
> > I'm brewing up a more thorough reply which goes
> into the matter
> > in some detail.  I'd like a few more days to work
> on it so that
> > I can try to adapt some of the tssp software to this
> type of
> > coil - not something we've looked at before.
> >
> > Meanwhile, have the proximity losses of this design
> been
> > considered?  If high Q is a design priority, would a
> helical
> > ribbon rather than a spiral ribbon not be a better
> proposition?
> > --
> > Paul Nicholson
> > --
> > _______________________________________________
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> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
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