## BPF design

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david753
Posts: 51
Joined: Fri Jan 16, 2004 1:01 am
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### BPF design

I am going to design a BPF, the center is 26MHZ, span is 2MHZ.
http://homepage14.seed.net.tw/[email protected]/t0284754/26m.doc
But, I found the value of L2 is 9UF.
How can I make it?
which type core? and how many turns?

k7elp60
Posts: 226
Joined: Wed Dec 05, 2001 1:01 am
Location: Ivins, UT
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### Re: BPF design

I think you have a typo, it should be 9uH. or about 9 microhenry. I would go the the Mouser cataloge and buy a adjustable one that has a nominal value that you want.

haklesup
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### Re: BPF design

Just google on "inductor design" and you will get many hits. Some pages just had formulas, others had tables or calculators but......<p>It soon became apparent to me that one could design a family of inductors all with the same value but with different shapes.<p>One formula I found:
L=D^2*N/1000(18*D+40*CL)<p>L=inductance
D=average diameter of coil
N=Number of turns
CL-Coil Length<p>Looking deeper, it seems one might want to keep N to a minimum to keep the total wire length minimal to reduce the DC resistance. <p>but are there any other gudelines for optimizing D and CL other than the space you have to mount it and the ease of assembly (for example if it is easy to use a pencil as a form, that would dictate the D)<p>Are there any frequency domain consiquences to designing one way as opposed to an equivilent shape? Is L constant for all frequencies. Does shape effect this property or any others.<p>I know adding a solid core increases inductance depending on the permitivity of the metal in the core making the formula more complicated. For now I just want to understand air core coils a bit better.<p>Perhaps someone can outline the thought process that they use for designing the specifics of an inductor.

russlk
Posts: 563
Joined: Thu Dec 06, 2001 1:01 am
Location: New Hampshire
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### Re: BPF design

I have use this equation for solonoid coils with good success:
L (microhenries) = ((n^2)*r^2)/(9*r + 10*l)
n = number of turns
r = radius of coil (1/2 diameter)
l = length of winding<p>Keep in mind that the leads of the coil are also part of the inductance which is not included in the equation!

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