Chris Maxwell said:
> I'm not sure what the case is with this particular cable. Maybe it's
> the result of a cable manufacturing that doesn't understand shielding
> theory; or maybe it's meant for a special purpose other than
> shielding.
Oddly enough the "well known" computer firm sells two ve
I've seen quite a few good replies to this thread with some fun EM
analysis. I'd like to offer a practical viewpoint (I know, I'm usually
the one that's throwing Math around...so I'll take the other viewpoint
this time)
I have my suspicions that some items are sold as "shielded" just so that
the
described in an earlier email.
George
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Ken Javor
Sent: Friday, September 16, 2005 4:33 PM
To: emc-p...@ieee.org
Subject: Re: When is a cable shield not a cable shield?
If we grant that an image plane can reduce radiated emissions when
uot;Adam Bullivant"
> Date: Fri, 16 Sep 2005 14:59:56 +0800
> To:
> Subject: RE: When is a cable shield not a cable shield?
>
> Hi Group. I'm a first time poster.
>
> An interesting discussion! I remember doing some research 10 years ago in a
> previous employment
n
Woodgate
Sent: 16 September 2005 14:10
To: emc-p...@ieee.org
Subject: Re: When is a cable shield not a cable shield?
Ken Javor wrote (in
) about 'When is a cable
shield not a cable shield?', on Thu, 15 Sep 2005:
> The reason for terminating the shield at both ends at high frequ
List-Post: emc-pstc@listserv.ieee.org
Date: Thu, 15 Sep 2005 16:41:12 -0700
To: owner-emc-p...@listserv.ieee.org
Cc: emc-p...@ieee.org
Subject: RE: When is a cable shield not a cable shield?
The principle is demonstrated by industrial induction heaters, where a few
seconds of 13 MHz eddy current
emc-p...@ieee.org
Subject: Re: When is a cable shield not a cable shield?
Ken Javor wrote (in
) about 'When is a cable
shield not a cable shield?', on Thu, 15 Sep 2005:
> The reason for terminating the shield at both ends at high frequencies
>(cable electrically long) is to contain
Ken Javor wrote (in
) about 'When is a cable
shield not a cable shield?', on Thu, 15 Sep 2005:
> The reason for terminating the shield at both ends at high frequencies
>(cable electrically long) is to contain the eddy currents on the
>interior of the equipment enclosure, of which the shield i
obert A. Macy"
> Date: Thu, 15 Sep 2005 20:27:32 -0700
> To: Ken Javor
> Cc: emc-p...@ieee.org
> Subject: Re: When is a cable shield not a cable shield?
>
> Ken,
>
> May be I don't understand what you are saying. My
> apologies. I thought you were saying th
flow due to Faraday Law
> induction, which is
> a vector phenomenon, and then the shield has to form a
> loop penetrated by
> the magnetic field vector, or it won't work.
>
> > From: "Robert A. Macy"
> > Date: Thu, 15 Sep 2005 15:27:54 -0700
>
lectricity has
been generated by the generator.
George
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Price, Ed
Sent: Thursday, September 15, 2005 4:41 PM
To: owner-emc-p...@listserv.ieee.org
Cc: emc-p...@ieee.org
Subject: RE: When is a cable shield not a cable shie
axial transmission line; the shield is the coaxial
>> transmission line
>> shield and return conductor.
>>
>>> From: "Robert A. Macy"
>>> Date: Thu, 15 Sep 2005 11:28:26 -0700
>>> To: Ken Javor
>>> Cc: emc-p...@ieee.org
>>>
n Javor
> Cc: emc-p...@ieee.org
> Subject: Re: When is a cable shield not a cable shield?
>
> Eddy currents exist everywhere the conductor looks like a
> shorted turn on a transformer.
>
> Imagine a perfectly balanced pair of wires, driven in a
> perfetly balanc
uch a way as to
> >> cause a magnetic field
> >> that opposes the originating field (Lenz' law). In
> order
> >> for the eddy
> >> currents to have sufficient magnitude to cause field
> >> cancellation, the
> >> shield mus
buildings becomes an
extension of the buildings it connects.
> From: "George Tang"
> Date: Thu, 15 Sep 2005 13:49:00 -0700
> To: "Ken Javor" ,
> Subject: RE: When is a cable shield not a cable shield?
>
> "Low frequencies" is really a relative term
nds of the
shield does not stop the eddy currents. This is why fields and waves are so
interesting.
George
From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of Ken Javor
Sent: Thursday, September 15, 2005 12:37 PM
To: emc-p...@ieee.org
Subject: Re: When is a cable shield not a cable sh
: Thu, 15 Sep 2005 11:28:26 -0700
> To: Ken Javor
> Cc: emc-p...@ieee.org
> Subject: Re: When is a cable shield not a cable shield?
>
> Yes, it can.
>
> The fibres are all shorted out making it a pseudo-metal
> plane.
>
> Plus, the loops of interest are pretty muc
Subject: Re: When is a cable shield not a cable shield?
>
> Ken Javor wrote (in
> ) about 'When is a cable
> shield not a cable shield?', on Thu, 15 Sep 2005:
>> I have a problem with this as well. A non-magnetic shield material
>> protects against magneti
perform this function.
>
> > From: "Robert A. Macy"
> > Date: Thu, 15 Sep 2005 09:16:09 -0700
> > To: "Hudson, Alan"
> > Cc: emc-p...@ieee.org
> > Subject: Re: When is a cable shield not a cable shield?
> >
> > Alan,
> >
Ken Javor wrote (in
) about 'When is a cable
shield not a cable shield?', on Thu, 15 Sep 2005:
>I have a problem with this as well. A non-magnetic shield material
>protects against magnetic field radiation by providing a path for eddy
>currents to flow in. The eddy currents flow in such a wa
Ken Javor wrote (in
) about 'When is a cable
shield not a cable shield?', on Thu, 15 Sep 2005:
>In fact it is not the concept of floating vs. grounding that is
>important here. It is the concept of enclosing the radiating circuit.
>Terminating the shield to an enclosure at both ends helps to
ot;Hudson, Alan"
> Cc: emc-p...@ieee.org
> Subject: Re: When is a cable shield not a cable shield?
>
> Alan,
>
> Think also in terms of magnetic fields, or "area loops".
>
> The area defined by the small loop between signal lines and
> ground lines now have rathe
elements, even if the entire enclosure is floating.
> From: Scott McMorrow
> Date: Thu, 15 Sep 2005 11:52:06 -0400
> To: "Hudson, Alan"
> Cc: "EMC-pstc (E-mail 2)"
> Subject: Re: When is a cable shield not a cable shield?
>
> Alan
>
> This would be
Alan,
Think also in terms of magnetic fields, or "area loops".
The area defined by the small loop between signal lines and
ground lines now have rather opaque metal plates over them.
Starting around 10KHz the conductive "shield" kills all
the magnetic fields coming out. Which were probably more
Alan
This would be no different than a floating metalic enclosure around any
piece of electronic equipment. You have parasitic capacitance
everywhere, and, in the case of a cable with such a metal jacket, the
coupling is quite high. Thus, everything is coupled to everything
else. In additio
>From an immunity point-of-view:
A totally floated shield is at best useless, at worst worse than no shield.
At the frequency at which it is a half-wavelength long, quite a bit of
current will flow in the middle, and quite a bit of potential will occur at
the ends. Both current and potential wil
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