From: Doug McKean (email@example.com)
Date: Wed May 30 2001 - 11:27:02 PDT
Looking at my Paul book, my mistake. Page 408 has
the E field produced by a loop as you stated. Such is
my myopic email writing ...
But, I still maintain by using this relation alone for the far
field, some factors would have to be exceedingly high since
the units are meters, amps. Using centimeters and milliamps
for typical board constructions, it's not enough to swamp
out the 10^-14 factor for trouble with emissions at 10 meters.
I've made my own magnetic and electric probes for probing
around on boards with a spectrum analyzer. A kluge I know,
but I do get very different readings depending upon the probe,
i.e. magnetic or electric. And I use that data to anticipate
possible problems with: locating possible emi problems with
boards, effects on victim boards at close proximity to source
board, I/O cabling issues, shielding effectiveness, chassis slot
construction especially possible slot effects, any grounding issues,
What I have noticed are near field effects (which can be quite
strong) on a board being transferred to circulating currents in
any shielding. This produces any number of emissions problems
with chassis shielding effectiveness and/or cabling problems.
This is not to say that near field measurements can predict
far field results either. I haven't been able to correlate that
at all. Nor do I know of anyone who can.
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