[Antennas] Inductors

[CubexCo@aol.com]

In a message dated 11/3/03 4:32:57 PM Eastern Standard Time, ve7hcb@rac.ca 
writes:

> If a have a cylindrical form (say 1in dia by 12 in+ long) and wrap wire 
> around the 
> circumference of the form with so many turns per inch ( 8 per in). Then I 
> would have 
> 
> L = 2 * pie * r * l * t/in  = 2 * 3.14159* 1 *12 *8 = 50.25 ft
> 
> Inductance = a**2 * n**2 /  (9a + 10 b) = 1* (12*8)**2/ (9 + 10*12) = 71.44 
> uh.
> 
> Now, if instead of wrapping the wire around the circumference, I loop the 
> wire from 
> one end to the other then back to the first end, then down to the second 
> end, etc 
> working around the circumference spacing the wire at 8 stands per in, I will 
> use the 
> same amount of wire.  What would the inductance be?
> 
> Breaking the form open and making a flat coil would give a preposterous 
> inductance.  How would the inductance be calculated?  Maybe easily measured.
> 
> Anyone know?
> 
> Chris opr VE7HCB
====================
Chris,
I have not address your question, but I did note that your early calculations 
are not correct if the dimensions you gave are accurate.  Quick look at your 
results - 50.25 ft of wire, that is over 600 inches, I don't think that will 
fit your form.  
I think the correct answer is base on the diameter (1") the length (12") and 
the turns per inch (8)  Maximum wire selenoid wound would be 12*8, or 94 
turns, and a length/turn (circumference) is PI * dia =Ct or total wire length = 
94t*Ct= 94*PI or about 295in (24.6ft).
You used the diameter instead of the Radius (r=.5)
I have not checked to see if the formula for inductance is correct.
Your second case is not as clear as to the form of the coil, but it sounds 
like you are winding end over end which nominally forms a rectanular (or 
prismatic) shape with the short sides being 1", and the long sides 12 in.  The wire 
per turn would be 1+12+1+12 or 14in per turn.(discarding corner or edge radii) 
so 295 in of wire would result in 295/14 = 21turns, this obviously doesn't fit 
a 1" x 12" prismatic shape, and the turns would have to be layered (21/8 
layers).

Now the confusion I have is with your description of "breaking the form open" 
 - I must have missed something above as I cannot envision that step.  And as 
a result my response may be off the mark.  Maybe you can clarify the "shape" 
of the second inductor case.

Regards,
Norman W4QN
Cubex Engineering

"The Power of a Cubex Quad"

<A HREF="http://www.cubex.com/">http://www.cubex.com/</A>



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