+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Newbie level 6
    Points: 796, Level: 6

    Join Date
    Feb 2010
    Location
    Ghent, Belgium
    Posts
    11
    Helped
    0 / 0
    Points
    796
    Level
    6

    Help me with tunning the crystal filter

    Dear all,

    Have anyone here have some experience b4 of tuning the crystal filter center frequency?

    As we know, the crystal filter has a very sharp passband bandwidth and very high Q. While, the crystal filter is also very hard to tune the frequency you want. I want to have a crystal filter at frequency 27.27273Mhz, while the crystal at this frequency is really hard to find. The closed crystal I could find is 27.3MHz.(By the way, I do not have the crystal on my hand, I do not know the exact resonance frequency)

    So can I ask anyone who could share the experience with me of tuning the crystal filter.

    Many thanks!

    Best,

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 34,356, Level: 45

    Join Date
    Dec 2004
    Location
    New England, USA
    Posts
    4,820
    Helped
    1349 / 1349
    Points
    34,356
    Level
    45

    Re: Tuned Crystal Filter

    Not a crystal filter expert, but my experience has been that the crystal can be used in a mode where it looks like a giant inductance. In that mode, you can externally pull the frequency a little with external inductance/capacitance. Maybe can pull it 50 KHz or so.



    •   AltAdvertisement

        
       

  3. #3
    Advanced Member level 5
    Points: 33,915, Level: 44

    Join Date
    Oct 2001
    Posts
    4,841
    Helped
    1436 / 1436
    Points
    33,915
    Level
    44

    Re: Tuned Crystal Filter

    Here is an example how to tune a ladder crystal filter.


    Beware, usually 27MHz crystals are actually overtone crystals with fundamental on 9MHz.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 5
    Points: 16,136, Level: 30

    Join Date
    May 2010
    Location
    Santa Barbara
    Posts
    2,832
    Helped
    840 / 840
    Points
    16,136
    Level
    30

    Re: Tuned Crystal Filter

    A quartz crystal alone could be "pulled" by external capacitor or inductor, but a filter composed of several resonators comprises also precisely adjusted coupling elements for a good response, most often, a band-pass. In principle, such filter cannot be tuned or its center frequency moved, without simultaneously varying all filter elements.
    To design a variable-frequency band-pass filters, use active filters with operational amplifiers; new types extend up to >1 GHz, and their gain can increase the filter pole-zero performance while it is easy to "tune" such filter.



--[[ ]]--