Several excellent ideas have been put forward on this phenomenon. Here is
my $.02 worth on the subject.
I have often been able to reduce the far-field emissions, based on the
reduction in near-field emissions. The important thing is to co-relate the
far-field and near-field emissions, by comparing their frequency spectrums.
It is possible that the 400 MHz clock you worked on with near field probe
may not be the real culprit. Another trace may be coupling the 400 MHz
clock noise to some cable, or one of the other signals, which is driven by
the 400 MHz clock, may be the real source.
Regards, Ravinder
PCB Development and Design Department
IBM Corporation - Storage Systems Division
Email: ajm...@us.ibm.com
***************************************************************************
Always do right. This will gratify some people and astonish the rest.
.... Mark Twain
marti...@appliedbiosystems.com@ieee.org on 09/14/2000 10:07:36 AM
Please respond to marti...@appliedbiosystems.com
Sent by: owner-emc-p...@ieee.org
To: emc-p...@majordomo.ieee.org
cc:
Subject: Near Field Versus Far Field
I am having a difficult time answering the following question for a
non-technical person. Hopefully, someone can put the answer into a
language
that a non-technical person can understand.
We have a 400 MHz clock and are failing radiated emissions at 10 meters by
10 dB
at 400 MHz. We bring the product back to our lab and start making
modifications
on the clock circuit and taking measurements with a near field probe. With
these modifications and measuring with a near field probe, we realize a 10
dB
reduction in emissions at 400 MHz. Why would we not see the same reduction
when
taking the product back to a 10 meter site?
Your help is appreciated.
Regards
Joe Martin
marti...@appliedbiosystems.com
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