# How to correctly simulate this filter?

I am trying to design a low-pass filter for a 24V, DC, 10A power line to suppress EMI, RF interference and noise in a bus. There is no ground(chassis). I am trying to simulate this filter that was tried in the bus and worked (the audio amplifier was noise-free). This filter is the filter on my previous question.

I couldn't calculate the cutoff frequency because of the common-mode chokes. Could you help me calculate?

I am trying to simulate it, however it doesn't seem right. Am I simulating it right?

Here are the schematics and graphs from LTSpice:

• You have high resonance peaks which might be due to no series equivalent resistors in the chokes. Even though you are using 10A rated chokes, they will have some resistance, which will damp the peaks. – Martin Oct 5 '11 at 12:11
• Thanks! This really damped the peaks. Now that I can see that this filter has -6dB at about 160 MHz. Still this doesn't seem right. – abdullah kahraman Oct 5 '11 at 12:41
• The filter you link has common mode inductors, while your simulation will have simple inductors. – Connor Wolf Feb 23 '12 at 11:27
• @FakeName I thought K L1 L2 1 is for simulating it as common mode inductor. How can I simulate common mode inductors? – abdullah kahraman Feb 26 '12 at 15:06
• @abdullah kahraman - I didn't see that. I would have thought a common mode inductor would have a different schematic primitive. Anyways, apparently you know more about SPICE them I. – Connor Wolf Feb 27 '12 at 6:24