Hi everybody,

I am designing a passband filter. I am definitely OK with the calculation and theory, but I end up with fancy values, like 1.92uF, etc. Actually, I am wondering what kind of inductor shall I take ? I've seen a bunch of different: Coils, toroidal, etc, even ones looking like resistors :S. What is the difference between this type of inductors and which one should I use ?

Thanks a lot,

c0

 

What is your application? Is this for radio frequency work?

 

Yes, this is a radio bandpass filter for ~300MHz.

 

It would be worth your while to post the designed schematic with values. A capacitance of 1.92uF at that frequency seems a little odd. The associated inductor values may be impractical ....?

 

Ok, it might not be the right value , I have the schematics at home. However, I was just wondering whether I should do the inductor myself or buy an existing one 0o ? There are so many differences in shape between these coils that I don't understand the difference and when/where to use them

 

Surface mount inductors seem to be the modern choice for the frequency of interest. But your choice will depend on how you intend to fabricate and test / tune the filter. That won't be a trivial task.

Anyway - maybe take a look at this link ...

http://vaedrah.angelfire.com/inductors.htm

 

Thanks t_n_k. I am asking the question, because it seems that the toroids have a pretty fast decreasing Q at high frequency. I'll dig into that.

 

To get reasonable values you sometimes do this:
http://en.wikipedia.org/wiki/Prototype_filter

You solve for the components values assuming something like 1F and then you can scale all the components to something practical based on your restrictions.

 

its not necessary to use an inductor you can use the following link
http://www.allaboutcircuits.com/vol_2/chpt_8/4.html