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Filters

CiaranM

May 19, 2012
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May 19, 2012
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I'm in need of a bit of help regarding filters. Specifically, filters with inductors.
I know how RC filters work, and I understand reactance, and that a resonant frequency is formed when capacitive reactance is equal to inductive reactance.
Some questions:
- what is the equation for a LC filter?
- what is the equation for a LRC filter? Is it RC's f=1/2piRC?
- is it possible for the resonant frequency to be different to the cut-off frequency?
- is it possible to increase the amount of resonance in a circuit? some sort of feedback, perhaps?

thanks.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
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May 8, 2012
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4,960
- is it possible to increase the amount of resonance in a circuit? some sort of feedback, perhaps?

thanks.

This is governed by the 'Q' factor of resonant circuit. The higher the Q the greater the resonant voltage developed across a tank will be. Q effects both parallel and series resonance. There are circuits known as "Q multipliers". Google it. BTW, whole hard cover text books have been written on filter design. It's a science unto itself. Particularly when dealing with RF, as input and output impedance is of paramount importance,

http://www.radio-electronics.com/in...f-filters/simple-lc-lowpass-filter-design.php

http://circuitcalculator.com/lcfilter.htm

http://www.corollarytheorems.com/Design/filter.htm
 
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