Re: [TCML] Why copper tubing for primary?

[Gary Lau <glau1024@xxxxxxxxx>]

Coax can be used for a primary but it's far from optimal, if one is shooting
for maximum performance.

Due to skin effect, it doesn't really matter what you do with the inner
conductor.  But the bigger issue is the woven nature of the stranded outer
conductor.  Skin effect will cause the current to constantly "gravitate" to
the outer strands of the weave.  But as a strand weaves back towards the
interior, the current following that strand will try to get back to the
exterior.  The shortest path to do this is by hopping from the now inner
strand to a different, outer strand, through any intervening resistive oxide
and plating layers.  This is why Litz wire has individually insulated
strands - to prevent current from hopping between strands with resulting
resistive losses.

Then there's the problem of tapping the insulated braid.  Doable, but not as
easily as good ol' refrigeration tubing.  In general, solid wire (or tubing)
is both electrically and mechanically superior to stranded, non-Litz wire.

Bob Wroblewski has built a small coil using only the intrinsic capacitance
of a coaxial cable primary coil as the primary capacitor, as a proof of
concept.

Regards, Gary Lau
MA, USA



On Fri, Aug 13, 2010 at 4:51 PM, Joe Mastroianni <joe@xxxxxxxxxxxxxx> wrote:

> Along these lines I've been wondering about coax for primary winding. I
> have a lot of rg214 around from my extreme dxing days and I have seen on
> various websites that credible people have used coax in this manner.
>
> I imagine one shorts the center to the sleeve connection to avoid creating
> a giant transmission line capacitor. Or does one calculate for resonance and
> leave one end open??
>
> Cheers
> Joe_______________________________________________
>
>
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