Hi,
I have a coil that is wound on a 1.125 inch diameter form and 3 inches
long space wound with 25 turns of 11 gauge aluminum wire...
I am trying to duplicate this coil only instead of using 11 gauge wire
I am using 12 gauge aluminum wire.
I was wondering if somebody could help me out and make sure my math is
right since I am unsure of how to go about making sure I match the
inductance.

I had this figured out once but mistakenly had the wrong wire
gauges...

Any help is greatly appreciated
Thank You

On Sep 21, 10:25 pm, Clayton wrote:
Hi,
I have a coil that is wound on a 1.125 inch diameter form and 3 inches
long space wound with 25 turns of 11 gauge aluminum wire...
I am trying to duplicate this coil only instead of using 11 gauge wire
I am using 12 gauge aluminum wire.
I was wondering if somebody could help me out and make sure my math is
right since I am unsure of how to go about making sure I match the
inductance.

I had this figured out once but mistakenly had the wrong wire
gauges...

Any help is greatly appreciated
Thank You

Back not so long ago when you posted a similar question on the antenna
newsgroup, Owen Duffy so kindly posted a url for an inductance
calculator, which I repeat here for your benefit:
http://hamwaves.com/antennas/inductance.html. It will do all the math
for you. Well, almost all. You still need to put your dimensions in
terms of millimeters, and make sure you enter the diameter of the coil
as the form diameter plus the wire diameter, so that it's the mean
coil diameter you enter.

Cheers,
Tom

I would just visually duplicate what the original looks like. It should
be fairly close and you can spread or squeeze the turns to "tune" it to
the inductance required.

Scott
N0EDV

K7ITM wrote:

On Sep 21, 10:25 pm, Clayton wrote:

Hi,
I have a coil that is wound on a 1.125 inch diameter form and 3 inches
long space wound with 25 turns of 11 gauge aluminum wire...
I am trying to duplicate this coil only instead of using 11 gauge wire
I am using 12 gauge aluminum wire.
I was wondering if somebody could help me out and make sure my math is
right since I am unsure of how to go about making sure I match the
inductance.

I had this figured out once but mistakenly had the wrong wire
gauges...

Any help is greatly appreciated
Thank You


Back not so long ago when you posted a similar question on the antenna
newsgroup, Owen Duffy so kindly posted a url for an inductance
calculator, which I repeat here for your benefit:
http://hamwaves.com/antennas/inductance.html. It will do all the math
for you. Well, almost all. You still need to put your dimensions in
terms of millimeters, and make sure you enter the diameter of the coil
as the form diameter plus the wire diameter, so that it's the mean
coil diameter you enter.

Cheers,
Tom


--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

Thanks Tom,
That calculator doesn't work for me for some reason. Every time I
tried to use it,it comes up with an error.
I have tried several different calculators but get varying answerers.

Hi Scott,
If My math is right I would need 23.5 turns of 12 gauge wire to reach
the same inductance as the original coil.

Sorry for what may seem like a repeat post,but for some reason I can
not seem to get comfortable with coils and inductance.

Thank You

On Sep 22, 9:47 am, Clayton wrote:
Thanks Tom,
That calculator doesn't work for me for some reason. Every time I
tried to use it,it comes up with an error.
I have tried several different calculators but get varying answerers.

Hi Scott,
If My math is right I would need 23.5 turns of 12 gauge wire to reach
the same inductance as the original coil.

Sorry for what may seem like a repeat post,but for some reason I can
not seem to get comfortable with coils and inductance.

Thank You

I just ran the calculator at the referenced web site. It suggests
that you will have a hard time telling the difference between 25 turns
of 11AWG and 25 turns of 12AWG, wound on the same form and to the same
net length. The calc for the 12AWG shows inductance about 0.3% higher
than for the 11AWG. I'd have guessed it would be slightly lower. The
SRF's and Q's are similarly close, by that calc.

My feeling is that you are worrying the problem to death...

Cheers,
Tom

Clayton wrote:
Hi,
I have a coil that is wound on a 1.125 inch diameter form and 3 inches
long space wound with 25 turns of 11 gauge aluminum wire...
I am trying to duplicate this coil only instead of using 11 gauge wire
I am using 12 gauge aluminum wire.
I was wondering if somebody could help me out and make sure my math is
right since I am unsure of how to go about making sure I match the
inductance.

I had this figured out once but mistakenly had the wrong wire
gauges...

Any help is greatly appreciated
Thank You

So long as the new coil is wound at the same pitch as the old coil
the inductance will be the same. Since you want to use a higher
gauge wire (thiner) this will be easy to do. The pitch, is of course,
the number of turns per inch. So if the old coil was close wound, the
new coil will be slightly space wound (air spacing between each turn of
wire).

ken scharf ) writes:
Clayton wrote:
Hi,
I have a coil that is wound on a 1.125 inch diameter form and 3 inches
long space wound with 25 turns of 11 gauge aluminum wire...
I am trying to duplicate this coil only instead of using 11 gauge wire
I am using 12 gauge aluminum wire.
I was wondering if somebody could help me out and make sure my math is
right since I am unsure of how to go about making sure I match the
inductance.

I had this figured out once but mistakenly had the wrong wire
gauges...

Any help is greatly appreciated
Thank You

So long as the new coil is wound at the same pitch as the old coil
the inductance will be the same. Since you want to use a higher
gauge wire (thiner) this will be easy to do. The pitch, is of course,
the number of turns per inch. So if the old coil was close wound, the
new coil will be slightly space wound (air spacing between each turn of
wire).

It's worth adding that the size of the wire is often specified because
either that's what fits on the coil form (ie if you need X number
of turns, a bigger guage won't allow that number of turns in the
space) or because there is reason for using heavier guage (such
as because it's carrying higher current, or you want it self-supporting).

Coils don't exist by themselves. To serve a purpose, they are associated
with capacitance, and that capacitance will allow for adjustment, and
may even require adjustment even for a "perfect coil" since there
will stray capacitance from the circuitry that never shows up in
a schematic, and stray capacitance from the coil itself.

Michael

Thanks Tom,
I went ahead and wound the new coil with the same amount(25)of turns
as the original and will go from there. Like you mentioned I think I
am over worrying it.
I have a Grid Dip meter I have been meaning to learn how to use so
maybe I will try and learn on this coil...

As for the inductance calculator,I have no idea why it never works for
me? Every time I have tried to use it,it gives me an error?

Hi Ken,
I am assuming that the new coil is going to be wound at the same pitch
as the original as the form its wound on has spiraled groves in it
that the wire sits in.

Hi Michael,
The coil is actually part of a trap on a 3 element tri-band beam that
handles full legal limit power.
so I am guessing that the slight change in wire(from 11 to 12
gauge)wont hurt anything.

Can any of you suggest a good book on coils,that includes theory,math
and all that good stuff?

I Appreciate all the help and Patience everyone
Thank You

On Sep 23, 10:21 pm, Clayton wrote:
....
Can any of you suggest a good book on coils,that includes theory,math
and all that good stuff?

Google "Grover Inductance Calculations" and you'll get loads of refs
and comments on Dr. Grover's book on the subject (as well as places to
buy it). Are you sure you really want to know THAT much about
them?? :-) If your library has the book or can get it, it's an
interesting one to have a look into. For coils (or for that matter
straight wires) at RF, you need to start considering things like skin
effect (where the current flows mainly at the surface of conductors)
and proximity effect (where the fields from a nearby wire affect where
current flows in the wire under consideration -- like how adjacent
turns of a coil affect one another).

A more reasonable place to start might be a text for a first college
course in electricity and magnetism. You'll learn enough about
inductance to have a very decent understanding of it, and if you
explore other topics there, you'll have the tools to understand a lot
more about RF circuits and fields in general.

Finally, nothing replaces actually doing things with coils (and other
parts), getting them to perform some function you want. I've done
quite a bit of work with coils over the years, and I'm still
learning. Last week, I spent some time working on a filter that uses
several coils of approximately 100 nanohenries each. I'm looking for
100dB and more out-of-band attenuation. I had to get very detailed in
my computer model to have it correspond reasonably well with measured
performance, including the "parasitic" effects of stray inductance and
capacitance--more so than I initially expected. In a lot of other
situations I deal with, those strays aren't nearly so important.
That's the sort of thing you'll probably learn better by "doing" than
by "reading."

Cheers,
Tom


Cheers,
Tom