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Butterworth bandpass filter question

Discussion in 'Electronic Components' started by TRABEM, Sep 11, 2005.

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  1. TRABEM

    TRABEM Guest

    I am trying to scale an existing front end receiver (butterworth
    bandpass) filter to a different frequency range. Unfortunately, it has
    a transformer in the original design, so I'm stuck. I also don't know
    how to handle the load presented by the active front end component
    other than it's probably not significantly reactive.

    The existing filter is for a 7 Mhz receiver, I'd like to have a
    similar filter design for 50 to 200 Khz.

    The filter components and transformer winding details are in the
    document at:

    http://www.amqrp.org/kits/softrock40/SoftRock40 Assy v1.pdf

    The input chip is an FST3126, spec sheet is at:

    http://www.fairchildsemi.com/ds/FS/FST3126.pdf

    The spec for the T30-2 transformer core is at:

    http://partsandkits.com/T30-2.htm

    I have aade filter design software, but it isn't allowing me to plug
    in the transformer into the design page of the software....so, I need
    to know it's equivalent circuit I think.

    The transformer winding details are on page 4 of the document and the
    schematic of the front end is page 9. Ultimately, I need new values
    for L1, L2, C20, C21 and C22.

    If someone can give me a reasonable guess as to the equivalent circuit
    of the transformer and the IC (U5), I can do the rest of the job
    myself using the aade filter software.

    Thanks,

    T
     
  2. maxfoo

    maxfoo Guest

    On Sun, 11 Sep 2005 12:14:11 -0400, TRABEM <> wrote:
    Get the free software program call RFsim99 lets you design buttrworth filters.
     
  3. Reg Edwards

    Reg Edwards Guest

    I am trying to scale an existing front end receiver (butterworth
    =====================================

    How do you know it is a Butterworth as distinct from other types?
     
  4. TRABEM

    TRABEM Guest

    A butterworth is a butterworth............in any discussion of the
    butterworth filter, you will see this schematic.

    Asking how I know it's a butterworth is a little like asking how I
    know a car is a car.

    However, I don't know it all.........perhaps it's closely related to a
    butterworth, but called something else???

    Let me know if I've made an error please.

    T
     
  5. Hello T,

    a Bessel filter would have the same structure. The value of
    the components define what filter type it is.

    Bessel: max. flat group delay
    Butterworth: max flat frequency response

    You can also make a filter with this structure which is anything
    between both types.

    Best regards,
    Helmut
     
  6. TRABEM

    TRABEM Guest


    Cool, didn't know that.

    At VLF, the inductances are becoming quite large, requiring a toroid
    core for even a simple inductor.

    What are the advantages/disadvantages of each type relative to
    inductor size requirements?

    Maybe I should be looking at a bessel instead of a butterworth.......

    GL to all.

    T
     
  7. maxfoo

    maxfoo Guest

    A Butterworth filter is a Chebyshev filter with No ripple in the passband.
     
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