Building the filter !

Discussion in 'Wireless & RF Design' started by cam0, Sep 3, 2010.

  1. cam0

    Thread Starter New Member

    Mar 23, 2010
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    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
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    What is your application? Is this for radio frequency work?
     
  3. cam0

    Thread Starter New Member

    Mar 23, 2010
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    Yes, this is a radio bandpass filter for ~300MHz.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    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 ....?
     
  5. cam0

    Thread Starter New Member

    Mar 23, 2010
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    Ok, it might not be the right value :p, 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
     
  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    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
     
    cam0 likes this.
  7. cam0

    Thread Starter New Member

    Mar 23, 2010
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    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.
     
  8. Ghar

    Active Member

    Mar 8, 2010
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    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.
     
  9. sat.astra

    New Member

    Apr 1, 2010
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