Designing a 30kHz Bandpass: Passive or Active?

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In summary, the conversation discusses the need for a bandpass with specific specifications, including a fixed center frequency of 30kHz, a narrow passband width, and steep slopes. The preference is for a passive design, but an active one using ferrite core inductors is also acceptable. The individual is open to adjusting the center frequency and is looking for recommendations for a commercial component or a book to help with designing it themselves. One suggestion is to use a crystal ladder filter with watch crystals, which would give a bandwidth of 1 Hz at a low cost. However, it is noted that this may not work due to high equivalent series resistance. The conversation concludes with a recommendation for a book on the topic.
  • #1
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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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  • #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


ISBN 9781-9050-8639-9 Size 210x297mm, 176 pages plus CD
 
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  • #3
Great idea! You never stop learning. Now I just need to see if I can get the passband wide and flat enough.
 
  • #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.
 

1. What is a 30kHz bandpass filter?

A 30kHz bandpass filter is a type of electronic circuit that allows a specific range of frequencies, centered around 30kHz, to pass through while attenuating all other frequencies above and below this range.

2. What is the difference between a passive and an active 30kHz bandpass filter?

A passive 30kHz bandpass filter uses only passive components such as resistors, capacitors, and inductors to create the desired frequency response. An active 30kHz bandpass filter, on the other hand, uses both passive and active components such as transistors or operational amplifiers to amplify the signal and improve the filter's performance.

3. Which type of 30kHz bandpass filter is better?

The choice between a passive or active 30kHz bandpass filter depends on the specific application and design requirements. Passive filters are generally simpler and cheaper to design and implement, while active filters offer better performance and flexibility in terms of adjusting the filter's parameters.

4. What factors should be considered when designing a 30kHz bandpass filter?

Some important factors to consider when designing a 30kHz bandpass filter include the desired frequency range and bandwidth, the type of input signal, the required attenuation of out-of-band frequencies, and the available budget and resources for the design.

5. How can I test and optimize a 30kHz bandpass filter design?

To test and optimize a 30kHz bandpass filter design, you can use simulation software or build a prototype and measure its performance. Adjusting the values of the components or changing the type of components used can help optimize the filter's response. It is also important to test the filter under different input signal conditions to ensure its effectiveness in real-world scenarios.

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