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Bandpass design

  1. Jul 24, 2010 #1
    I need a bandpass with the following specs:

    Center frequency around 30kHz fixed.
    Passband width a few Hz
    Steep slopes, phase doesn't matter
    preferably passive but active would work too especially if it spares me from inductors with ferrite cores (we have stray magnetic fields...)

    Can anyone recommend a design? I am somewhat flexible with the center frequency so if there is a commercial component for a few hundred dollars that would be great.

    Also: What is the best book if I have to design it myself?
  2. jcsd
  3. Jul 25, 2010 #2
    Crystal ladder filter using 32.768 kHz watch crystals will give you around a 1 Hz bandwidth. 3 or 4 crystals and a few capacitors.. total cost = peanuts.

    Featured in Technical Topics by Pat Hawker.

    Scroll down..

    http://www.rsgbshop.org/acatalog/GB2RS.html [Broken]

    ISBN 9781-9050-8639-9 Size 210x297mm, 176 pages plus CD
    Last edited by a moderator: May 4, 2017
  4. Jul 25, 2010 #3
    Great idea! You never stop learning. Now I just need to see if I can get the passband wide and flat enough.
  5. Jul 28, 2010 #4
    Turns out it didn't work. Probably because of the giant equivalent series resistance of 35kOhm. I used MHz crystal software to design the filter and those have 50 Ohm or so. If you have a working design please let me know.
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