[Lowfer] Coil question - Bowers

[Lyle Koehler]

First of all, I need to clear up some confusion regarding wire spacing. I
think in terms of center to center spacing between turns, while Bill Bowers
talks about spacing between wire edges. Bill's "single wire" spacing and my
"two wire diameters" are really the same thing. Reg Edwards uses the ratio
of "wire diameter to winding pitch", which would be 0.5 for what I call two
wire diameter spacing. There, I'll bet that really helped!

Bill Bowers' experiments, as reported in the July 1996 LOWDOWN, did not show
a huge difference in Q between no spacing and "single wire" spacing between
turns at a frequency of 200 MHz and a total inductance of 1 millihenry. When
I plug the coil dimensions into Brian Beezley's COIL.EXE program (which used
to be supplied on the disk that came with the ARRL Handbook), the spaced
solid-wire coil comes out with a Q at 200 kHz about 1.5 times that of an
unspaced coil. Bill Bowers' conclusions in the LOWDOWN article are:

"If you are going "all out" for maximum Q at LF then get the biggest #44 or
#42 Litz wire possible and design the coil with no spacing between the
turns. If you are using solid wire then the classic one diameter spacing is
best."

I think Bill and I are saying the same thing.

By the way, when I made my own theoretical calculation of the diameter to
length ratio that gives maximum inductance for a given wire length, the
actual ratio was 2.225:1. And I erred earlier in implying that this applied
only to spaced coils. The calculation was based on the simplified expression
for the inductance of a single layer solenoid, and the optimum form factor
is independent of wire spacing.