QUOTE: "And I don't think that 92dBuV/m is a high field strength to be
emitted by a PC placed nearby, or for a non-compliant laptop at 10 metres."

You may not think so, but I am sorry, the numbers just don't add up.  92
dBuV/m at 10 meters implies an effective radiated power of 5.3 mW.  Consider
that the source is not an intentional antenna.  It will have no more
directivity than a dipole and its efficiency will be much less since it
isn't matched to the source.  If we simply assume no gain (meaning matching
losses just offset directivity) , that means 5.3 mW of rf power are emitted
from the EUT or its attached cables.  If one makes the reasonable assumption
that it is common mode rf current which is radiating, then the potential
associated with rf power will be a small number of millivolts (in the
frequency domain).  This in turn implies a significant fraction of an Ampere
of common mode rf current.  A highly unlikely situation!  Once again, with
an impossible conclusion, either the assumption or the logic must be wrong.
You can choose to disbelieve, but please point out where the logic has gone
awry.  You have several times cited Mr. Woodgate for non-constructive
criticism.  Now I am asking you, don't give more hearsay: explain where my
physics is incorrect.  We are engineers here, not pollsters.

And if you are saying that specification level compliance at 10 meters can
scale up to 92 dBuV/m nearby, that is either false or misleading depending
on the frequency range.  At the low end, say 30 MHz, the area subtended by
position near the offending PC isn't large enough to efficiently radiate or
couple the field (the wavelength is 10 meters, and the other gentleman's
antenna factor calculation assumed a tuned dipole antenna in order to get a
small antenna factor).  So the field will not scale up  as per your
prediction, and the pickup mechanism will be nowhere near the antenna factor
that gentleman calculated.  In fact at 30 MHz your antenna factor will be on
the order of 20 dB or worse (assuming the mutual coupling length to be 1 m).
At the high end (near 1 GHz) you could be in the far field in close and the
field could scale up to a value of 92 dBuV/m, but the antenna factor of a
matched tuned dipole at 1 GHz is 26 dB so the potential from that perfect
antenna is 92 dBuV/m - 26 dB/m = 66 dBuV or 2 mV.  If you consider that any
signal with information content carried by 2 mV is shielded, the issue
becomes, once again, a non-problem.



on 1/6/02 10:43 AM, cherryclo...@aol.com at cherryclo...@aol.com wrote:

Snip:  And I don't think that 92dBuV/m is a high field strength to be
emitted by a PC placed nearby, or for a non-compliant laptop at 10 metres.

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