> Ah yes.. but manufacturing technology has advanced quite a
bit since the
> days of Terman. It's all well and good to assert that
1000kc was the
> practical limit in Terman's day. However, I wonder (not
too much, but just
> curious) what today's practical limit might be.
The nice thing about my job is I've always been paid to
measure things like this, and manufacturers and vendors give
me sample parts.
As I've said, I've never found a case above 300kHz (the
lower limit of my RF impedance test sets) where Litz wire
has decreased impedance, ESR, or increased Q in the same
form factor when replacing solid copper wire. Never.
I can't imagine stranded wire being better than solid wire
for ground impedance when the diameter is the same, because
it never is better for RF from the BC band on up. It is
never better at DC either for a given OD.
As a matter of fact when I modified a KW Hustler mobile
loading coil for 75M by rewinding it with the same diameter
solid enameled wire instead of the Litz wire and make no
other changes Q increases about 1.6-1.7 times.
I've seen Litz wire used in small LF switching transformers,
but never measured one A-B with enameled wire the same
diameter for ESR. So I don't know where Litz wire improves
things. I do know the DC resistance (for a given wire
diameter) is higher with Litz wire and the 300kHz and higher
resistance is higher in any application I've tested, but
there might be a sweet spot in some applications.
My transformer book claims it only helps reduce eddy
currents in the copper, nothing else. I tend to thing that
is correct based on what I've measured.
I'd stay away from any stranded wire in lightning grounds
unless there was no other choice. I think it is asking for
trouble.
73 Tom
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