[SI-LIST] Re: Traces don't cause EMI - really?

  • From: "Brent DeWitt" <bdewitt@xxxxxxxxxxxxx>
  • To: <leeritchey@xxxxxxxxxxxxx>,"Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
  • Date: Sun, 12 Oct 2003 19:44:32 -0600

Hello Lee,

I suspect much of the difference of opinion lies (as often is the case) in
subtleties of the English language.  If, in your statement, the words
"matched transmission lines" had been exchanged for "traces", I doubt anyone
would disagree.  In the extreme devil's advocate case, the trace could be a
resonant patch antenna over a ground plane.  Clearly not what you intended,
but a pretty good radiator.  As an intermediate case, I expect you would not
disagree with the concept that mis-matched transmission lines, even over a
continuous ground plane, may radiate significantly.

I have read and agree with Doug Brooks' well developed paper, but I'm not
sure it fully covers what Charles is concerned with.

With respect,

Brent G DeWitt
GE Medical Systems

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Lee Ritchey
Sent: Sunday, October 12, 2003 7:00 PM
To: Grasso, Charles; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Traces don't cause EMI - really?


Charles,

One of the papers I refer to is on my web site as well as That of Doug
Brooks.  It is titled "90 Degree Corners, The Final Turn".

The measurements were made in the lab at UMR.

If there is data out there that contradicts this, it would be good to share
it.

It's not hard to take a near field probe and run it along traces that are
on outer layers of a PCB with solid planes and get similar answers.

Lee


> [Original Message]
> From: Grasso, Charles <Charles.Grasso@xxxxxxxxxxxx>
> To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
<si-list@xxxxxxxxxxxxx>
> Date: 10/10/2003 9:20:28 AM
> Subject: [SI-LIST] Traces don't cause EMI - really?
>
> Lee,
>
> I was thumbing through some of the diff pair thread and ran across
> this comment that you had made:
>
> "Second, traces that run over continuous planes don't cause EMI,
> differenrtial or otherwise. Again, there are many papers that demonstrate
> this as well."
> I am sure you didn't mean this. There a many papers, notably by Bob
Dockey,
> that clearly
> show the diople-like profile of a trace over a continuous ground plane.
The
> paper
> also showed that, depending on the size of the board, the emissions can
> exceed the
> FCC Class B limits - thats one trace over a continuous ground.
>
> Can you please expand on your comment ?
>
>
> Best Regards
> Charles Grasso
> Senior Compliance Engineer
> Echostar Communications Corp.
> Tel:  303-706-5467
> Fax: 303-799-6222
> Cell: 303-204-2974
> Email: charles.grasso@xxxxxxxxxxxx; <mailto:charles.grasso@xxxxxxxxxxxx; >
>
> Email Alternate: chasgrasso@xxxxxxxx <mailto:chasgrasso@xxxxxxxx>
>
>
>
>
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