Re: [SI-LIST] : Conducted noise emission diagnosis device

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From: Patrick Lawler (
Date: Mon Apr 24 2000 - 09:39:32 PDT

One version involves resistively summing the two LISN signals, and
feeding the result to the EMC analyzer. Summing removes the
Differential Mode portion, leaving only Common Mode signals:

LISN1 signal --+---R1----+
                | |
                R2 |
                | +----R1----> To 50 ohm EMC receiver
             ground |
LISN2 signal ---+---R1----+
R1=16.7 ohm
R2=50 ohm

Resistor matching and symmetrical circuit layout is crucial for proper

Another method involves RF transformers to sum (leaving Common Mode)
or difference (giving Differential Mode) the LISN signals.
Mini-Circuits ( has parts that can do
this. Look for Power Splitters/Combiners - 2 Way - 0 degree/180 degree
I haven't tried this method.

On Fri, 21 Apr 2000 13:27:30 +0800, wrote:
>I am looking for a device that will differentiate the dominant component(either
>common-mode or differential-mode current) in the total conducted noise emission
>current of a product measuring through its' power cord using a LISN.
>I called this device "common/differential mode current separator". In conducted
>noise emission measurement, both common-mode and differential mode noise
>current are measured by LISN and the LISN can't tell which mode is the dominant
>I came across a paper by Clayton Paul and Keith Hardin which explain the
>usefulness of a separator like this that would identified the dominant current
>from the total current. Hence, the correct capacitor value(either X-caps or
>Y-caps) can be changed accordingly so to reduce the overall conducted noise.
>The book by Clayton Paul "Introduction to Eletromagnetic Compatibility" has
>also mention about this device.
>I have contacted a few persons trying to look for the person who have actually
>built this separator himself and I am also looking for any vendor who have this
>product for sale. So far, my effort has yield no results.
>Can anybody point me to the right person so that i can try to built this
>separator myself. Any other suggestion and comments are greatly appreciated.

Patrick Lawler
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