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 Radio and Communications Discussion forum for all aspects of RF and communication engineering, including antennas, modulation regimes, RF circuits and filter design, and telematics.

#1
03-23-2011, 09:51 PM
 turkeybuzzard New Member Join Date: Mar 2011 Posts: 3
LC bandstop theory

Hi -- I'm a novice and am trying to work out a theoretical problem. I put this question here because I figure you guys are the LC filter experts:

1. If I have a ideal AC source (at frequency f) connected to a series consisting of R,F,R,F,R (where Rs are equal resistance and Fs are LC parallel band stop filters tuned to frequency f) then what's the current across the resistors and what's the oscillating current inside each F. Is there no voltage drop across the Rs at the resonant frequency? Are the resonance currents inside the two Fs equal?

Here's the circuit:

http://dl.dropbox.com/u/7372632/Circuit.pdf

Dave
#2
03-25-2011, 06:33 AM
 t_n_k Senior Member Join Date: Mar 2009 Posts: 4,649

If these are all ideal elements one would expect zero source current at resonance. Each parallel stop filter would see half the source voltage with two such branches. If there were three branches each would support 1/3 of the source voltage. So each parallel branch element would have a current proportional to the source voltage. The currents in the L&C components would be of equal magnitude but exactly out of phase at resonance.
#3
03-25-2011, 07:42 AM
 turkeybuzzard New Member Join Date: Mar 2011 Posts: 3

T_N_K thanks for the clear response ... that makes sense.
#4
03-28-2011, 04:58 AM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 18,524 Blog Entries: 5

This is very similar to a thread (including the image) in the electronics chat area.

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 Tags bandstop, design, filter, oscillating, rlc, theory

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