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Thread: Notch filter at 125MHz

  1. #1
    namtey Newbie
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    Aug 2009
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    Notch filter at 125MHz

    I need to design a notch filter that blocks 125MHz (subharmonic) but passes 250MHz (fundamental). I am relatively new to high frequency filters and was hoping someone could offer some advice on what topology would be best for this type of filter? Active/passive/lumped/distributed/chip solution?


  2. #2
    JimB Excellent JimB Excellent JimB Excellent JimB Excellent JimB Excellent JimB Excellent
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    You give no context for where or how this filter is to be used, but any solution will almost certainly be a passive filter.

    One filter which is very easy to implement at these frequencies is the "Quarter Wave Stub".
    Take a length of co-ax cable, quarter of a wavelength long at the frequency to be attenuated, connect on end to the place where you want the attenuation and leave the other end open circuit. This will present a short circut at the quarter wave frequency and an open circuit at twice the frequency.

    JimB
    Experience is directly proportional to the value of the equipment ruined.

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