FreeLists / si-list / [SI-LIST] Re: EMC Issue at 266 MHz

["Knighten, Jim L" <JK100005@xxxxxxxxxxxxxxxx>]

The postings about the lack of half-wave symmetry creating even harmonics
are true.

Here is something different to think about: even harmonics are often
evidence of noise on the PCB power bus (power/ground planes).  The
professors at University of Missouri-Rolla teach this. If so, perhaps you
have inadequate decoupling.

_____________________
James L. Knighten, Ph.D.
Teradata, a division of NCR                 http://www.ncr.com
17095 Via del Campo
San Diego, CA 92127
tel: 858-485-2537
fax: 858-485-3788


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Jean_Pierre.Bouthemy@xxxxxxxxxx
Sent: Monday, March 01, 2004 10:24 AM
To: si-list@xxxxxxxxxxxxx
Cc: Guy.Barange@xxxxxxxxxx; Herve.Wattier@xxxxxxxxxx
Subject: [SI-LIST] EMC Issue at 266 MHz

Hi SI experts,

I have a question regarding an EMC issue.
Our system has failed the EMC radiated emissions with a 266.6 MHz emission
+3dB above Class A gabarit !
We have many 66.66 MHz clocks in our system, made with 50MHz oscillator
feeding a PLL, whose 400 MHz VCO frequency divided by 6 gives 66.66 MHz.
My question is the following:
I could understand an emission at the odd harmonics:
 - 66.66MHz x 3 =   200 MHz or,
- 66.66MHz x 5 = 333.33 MHz or,
- 66.66 MHz x 7 = 466.66 MHz or,
- so on ...

But I don't understand why we have problem with the fourth harmonic : 66.66
MHz x 4 = 266.6 MHz !!
=> Does anyone have an idea ?
=> Is it possible the 266MHs emission doesn't come from our 66.66MHz
clocks?
=> In this case wher could it be from?

Thank you for your help.
Regards.

Jean-Pierre Bouthemy


--------------------------------------------------------------------
Jean-Pierre BOUTHEMY
Hardware Design Engineer
ALCATEL - Mobile Networking Division (MCG)
Mobile Core R&D
+33 (0)2 99 26 08 18
mailto:jean_pierre.bouthemy@xxxxxxxxxx
--------------------------------------------------------------------


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu