FreeLists / si-list / [SI-LIST] Re: Emission level vary for same type of SATA cables but different vendors

["Eric Bogatin" <eric@xxxxxxxxxxxxxxx>]

To find the possible root cause of the EMI, I would look at mode conversion
and the quality of the connectors.

A significant source of EMI from cables is the intra-pair length skew in
each pair of cables. If the length of the two signal lines that make up a
pair are not matched, they will convert some of the  differential signal
into common signal, which will radiate.

If your SATA is 3 Gbps, the unit interval is 330 psec. 

If the rise time is 10% the unit interval, then when the intra-pair skew is
> 10% the UI you will have a common signal pulse height comparable to the
diff signal.

This is 30 psec of skew, or a length difference of about 180 mils. You need
to keep the length match between lines in a pair much lower than 180 mils. 

If you have a 4 port VNA, you can measure the SCD21 component of each cable
and compare the amount of mode conversion. Your high EMI cable may have a
larger mode conversion.

The second area to look at is the connector. In a shielded cable, it takes
mode conversion and a non-360 degree connection for the return path, to
drive EMI.

Check the clam shells and return path connections inside for the connectors
of each cable.

--eric

**************************************
Dr. Eric Bogatin, President
Bogatin Enterprises, LLC
Setting the Standard for Signal Integrity Training
26235 w 110th terr
Olathe, KS 66061
v: 913-393-1305
f: 913-393-0929
c:913-424-4333
e:eric@xxxxxxxxxxxxxxx
www.BeTheSignal.com 
Fall 2007 Signal Integrity Training Institute
EPSI, SIAA, BBDP
Oct 8-12, 2007, San Jose, CA
**************************************** 
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Kunal Sabavat
Sent: Tuesday, October 02, 2007 9:26 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Emission level vary for same type of SATA cables but
different vendors


    Hello,
   
  I am seeing different levels of EMI measured values from lab for same type
of SATA cables but from two different vendors. One of the vendors cable
shows much higher EMI values compared with another vendor cable. measurement
setup is same for two vendors cables. I still don't have full measurement
report. these are SATA internal cables, length of the cable is half meter.
   
  Can someone explain what could be wrong with the cable showing higher EMI
level? Taking cable TDR Impedance scan will help us understand?
   
  --
  Goutham

       
---------------------------------
 Unlimited freedom, unlimited storage. Get it now

------------------------------------------------------------------
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.net

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.net

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