Amund,
Cortland may be right, a chamber 'may not' be needed, high ambient
considerations to be put aside for the moment, even if the emission is
measured to be on the " 24dBuV/m @ 3m, freq.band 155MHz-165MHz". I am just
curious, what are the limits (or standards) are you trying to meet? From
what I read here, is it CISPR22 (or EN 55022) or something like that (Class
B) scaled back to 3 m? I note that it is about 20dB below FCC limits for
class B (at 3m).
If it is a single frequency line emission you can use a home made E or H
field probe and work in the near field. Douglas Smith (who post frequently
in this forum) have some good articles on DIY 1Ghz probes.
You would need a E-field probe to 'sniff' out the CM portion of the
emission and a H-field 'loop' to sniff out the offending loop before you
can hug a 'return wire' to the offending signal line to cut the return loop
down to size. I like to use the (thinisy, i.e. small gauge) wire-wraping
wires for this.
Good luck and hope that EMC don't always meant that it lead to Even More
Coffee for the all nighter.
Tim Foo
Cortland Richmond
<72146.373@compuserve. To:
"[email protected]" <[email protected]>, ieee pstc
com> list <[email protected]>
Sent by: cc: (bcc: Wan Juang
Foo/ece/staff/npnet)
owner-emc-pstc@majordo Subject: Decoupling -
capacitor values (ESR, layout, CM filter)
mo.ieee.org
04/20/02 05:39 AM
Please respond to
Cortland Richmond
Cortland Richmond <[email protected]>
04/20/02 05:39 AM
Amund,
You do not HAVE to be in a chamber to keep working on this. Since there is
only one Vcc pin (which processor IS this? - be SURE there is only one Vcc
pin; you may have an unfiltered, unconnected Vcc pin or two) you are
limited in how many capacitors you can attach to it. This doesn't matter;
if you filtered power, and got 7 dB, you've done there what CAN be done
there and should look look at other things.
Troubleshoot the board. I too have thrown solutions at problems without
knowing what exactly was wrong. It takes too long and costs too much.
Find the source. A small 'scope probe, with the end taped over, makes a
serviceable E-field probe. <snip>
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