[Lowfer] Litz source>Price quote...

[Ed Phillips]

WE0H wrote:
> 
> Maybe there is a way to wind Litz coils and another different way to wind
> single conductor wire coils. We know how to get a single wire coil to work,
> but maybe there is something special to winding a Litz coil to get a way
> higher Q.
> Hmmm,
> Mike>WE0H

	"Special windings" probably have a significant effect.  The navy
surplus loading coil I use here at IZJ has a form about 7" diameter and
a winding length of about 5" (just eyeballing it across the room).  The
winding is three layers of litz.  I don't have the measurements handy,
but seem to remember the Q is about 350 at 180 kc.  The turns are built
up progressively in a winding method called "bank winding", which was
used to minimize the losses due to inter-turn capacitance.  I just
pulled out my second edition (1937) of Terman to look at his material on
"coils".  Chapter 2 has a lot of good information on methods of coil
winding & coil geometries and their effect on Q.  In Figure 21, page 21,
he compares the Q's of two coils "identical in every way except that one
is wound with solid wire and one is wound with litz of approximately the
same cross section.  The coil had a diameter of 6.3" and a winding
length of 6.1" and the inductance was 480 uH.At 200 kc the Q of the coil
wound with #18 wire is about 350, while the Q of the 96-38 litz wire is
about 700.  The Q of the latter peaks at just under 900 at 390 kc, while
the Q of the former has a maximum of about 480 at 520 kc.  The DC
resistance of the litz wire was 0.72 ohms, while the resistance of the
solid wire was 0.62 ohms.  Unfortunately he doesn't describe the coil,
but I suspect it was a single-layer solenoid.  Easy enough to figure out
from the inductance, wire size, and winding length but I'm too lazy.

	Upon looking at this book more carefully I think it would be good
reading for someone interested in the design of coils, both because of
the construction and performance stuff in the beginning and many
inductance formulae in Appendix A.  Since lowfer RF technology (not
modulation and reception techniques) goes back to the beginning of the
century, so a 1937 book should have represented the "state of the art". 
Standard text book, so should be plenty of copies around.  For those who
don't know, Terman was an active ham at the time he entered Stanford and
probably remained so for some time.

Ed

Ed