Designing a 30kHz Bandpass: Passive or Active?

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A bandpass filter design is needed with a center frequency around 30kHz, a few Hz passband width, and steep slopes, with a preference for passive solutions to avoid issues with ferrite core inductors. Suggestions include using a crystal ladder filter with 32.768 kHz watch crystals, which can achieve a 1 Hz bandwidth at low cost. However, challenges arise due to high equivalent series resistance, impacting performance. The discussion also seeks recommendations for commercial components or books to aid in self-design. Overall, the goal is to find an effective design that meets the specified criteria.
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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?
 
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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


ISBN 9781-9050-8639-9 Size 210x297mm, 176 pages plus CD
 
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Great idea! You never stop learning. Now I just need to see if I can get the passband wide and flat enough.
 
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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