[Boatanchors] Making coils

[Gary Schafer]

Doesn't that wire (Litz) also have to be specially braided and of course
individually insulated so that each strand has an equal length exposed to
the outer surface of the bundle in order to get the maximum effect of
lowering the skin resistance?

Skin effect is thought of as being most important at high frequencies but it
is important at low frequencies also as Ron points out in the 100 kc
transformers. It was quite commonly used to wind 50 kc IF transformers.

73
Gary  K4FMX


Ron wrote:

> Hi Kees
>
> I use multistranded wire for the switching power supplies that we design
> here. Although it is only used to 100 Khz it does lower the series
> impedance due to skin effect and keeps the coil cooler.
> In your design , you will need to use wire no larger than twice the skin
> depth.
> ---
> Ron
>
> Sandy and Kees Talen wrote:
>
> > I'm playing around with some homebrew RF coils, RF
> > transformers, etc and will put together a coil winder in the
> > near future.
> >
> > My question is about wire. I have plenty of magnet wire up to
> > #38AWG (from good ol' swapmeets), however, the earlier
> > aplications used Litz wire but the "modern" (60's) JW Miller
> > coils seem to use magnet wire. What are the advantages ?
> >
> > Since the Litz wire is multistrand, the surface area is increased
> > which should improve it's capabilities at higher frequencies
> > due to "skin effect", the coil "Q" may be higher because of this,
> > and since it's not "round" it would lay in place better. Any other
> > reasons ? Is the main reason for the pattern winding to keep
> > the turns in place ? In other words, if you were winding on a
> > spool, you would be OK by just winding uniformly ? The
> > drawback would be finding the small stuff at a reasonable price.
> >
> > Magnet wire is cheap, might require the use of bobbins to get
> > it to stay in place (although JW miller solved this with enough
> > adhesive), and maybe multiple strands of #38 has the same
> > effect as Litz wire. Would it have to be twisted ? Is the only
> > reason for the winding pattern to keep turns in place ? Any
> > other comments ?
> >
> > 73s  Kees K5BCQ
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