On May 11, 6:29*pm, "Tom Donaly" wrote:
K7ITM wrote:
On May 11, 2:09 pm, wrote:
Hi Richard,

I wont even attempt to answer the "intimidating" questions - they're
far too tough for me!

But just a couple of comments:

1) The change in coil size when I swapped from a base-loaded to a mid-
loaded model was nothing more than a convenience to reduce the total
number of segments and reduce the computation time. It was not borne
out of any electrical considerations, so please don't read anything
more than that into it. In retrospect it was a silly thing to do
because it has probably introduced a "red herring".

2) You suggest that the Corum method has little utility. However, the
inductance calculator based on the method appears to give usefully
accurate predictions of "equivalent lumped reactance" and SRF (jury
still out on that one). If that calculator was not available, it seems
to me that designing a coil for something like a mobile whip loading
application would require tedious iterations of the helix generator in
EZNEC.

73,
Steve G3TXQ

For what it's worth, I've been using a coil program for quite a few
years now that is able to calculate the performance of a coil based on
a helical transmission line model. *It was developed out of travelling
wave tube theory. *It turns out I discovered a bug in the program and
reported it to the author, who very kindly corrected it. *I've come to
trust it to come up with answers that are very useful in an
engineering sense. *I would not expect it to tell me inductance or
other parameters (e.g., first parallel self resonance and first series
self resonance) accurately enough to be used as a precision lab
standard, but that's not what I use the program for.

When I became aware of the HamWaves web page, I was curious about how
well its answers compared with the ones I'd become used to trusting.
They do differ a little, but again, for what I do with them, I trust
them both. *Either one will provide results I can use to wind a coil
for a filter and know I won't have to much to adjust the coil to being
"right on." *And in fact, I also found a very small bug (or at least
an anomaly or inconsistency) in the HamWaves calculation, and reported
that to Serge, who likewise very graciously acknowledged it and who I
believe corrected it.

So I'd strongly support your thought that the HamWaves calculator
provides useful results. *Understand that they won't be perfect, but
also understand that you may have trouble making measurements accurate
enough to know how much they are in error. *But for almost everything
I do with coils, what I care about is whether the filter or tank
circuit or antenna in which the coil is used actually works like I
want. *My trust in these programs comes from being able to build a lot
of filters over the years that all work like I designed them to work,
with very little effort to tweak the coils I built per the programs'
predictions. *I'll adjust my expectations if I ever find cases where
the programs lead me astray.

Cheers,
Tom

Hi Tom,
* * * * *A testimonial from you goes a long way toward building some
trust in ON4AA's coil calculator. I was concerned because I haven't seen
much in the way of empirical data to substantiate the claims made for
it. I would have thought that the creators would have at least provided
a link to some data, or to a description of their own coil-making efforts..
73,
Tom Donaly, KA6RUH

Well, I'm flattered, but I'd invite you and anyone else here who might
build coils for practical purposes to report back how that calculator,
or any other, worked for them. The homebrew newsgroup might be a
better place to do that. And if you think you've come up with a
situation where any calculator seems significantly in error, don't be
shy about reporting it to the author or maintainer of the calculator.
I've found most to be quite happy to hear about bugs, especially if
they are well documented, if they are told in a nice way.

I tend to not push the limits on coil calculations, because I know
that I'll get the best volumetric efficiencies with coils over a
relatively small range of diameter-to-length ratios, and for air-core
solenoid RF coils used between a couple MHz and a few hundred MHz, I
know what physical size I'll need for any particular required Qu. So
you very well may find cases of more extreme D:L ratios where a
calculator I've learned to trust isn't so hot -- and honestly, I'd
love to know about such limits.

Cheers,
Tom


Cheers,
Tom