Many a good conversation veers off onto other interesting threads
and indeed this is one of the things I enjoy about reading the various
messages even those that have no direct impact on me.
Sorry you felt ignored, although as I followed it the first
responses did address the issue. It sorta can't be done, but you might want
to try CE emissions as a way to correlate from your site data to the OATS 10
meter.
Not trying to get your hackles up, but I would hate to see good
discussions get stymied just because they wander from topic to topic.
Take care
Gary
-----Original Message-----
From: Paolo Roncone [mailto:[email protected]]
Sent: Wednesday, January 17, 2001 3:08 AM
To: Lothar Schmidt
Cc: EMC-PCST (E-mail)
Subject: RE: Site Correlation
Good point Lothar,
it was about time that the original technical grounds and limitations of CE
method were brought up.
Just one additional point: with the ever increasing operating frequencies
of many electronic products, box and/or PCB level radiation is getting more
and more important vs cable radiation (and as a by-product cable layout
should weigh less in measurement uncertainty).
One last point: I was a bit perplexed by the way this thread shifted from
the original question. I myself stepped in early with a question about
fully-anechoic vs semi-anechoic pre-compliance chambers but then the
subject switched to the CE vs RE issue and nobody gave a damn about me..
Paolo
At 11:28 AM 1/16/01 -0800, Lothar Schmidt wrote:
>I have the feeling that different issues are mixed in this discussion.
>
>supposed that CE vs. RE methods is the issue, I can give you some
historical
>information. The CE method is used as a simplified method for the radiation
>of the tested device.
>The CE method was used for devices which have to met several conditions
>1. the cable length was long compared to the size of the device ( the
>longest side should not be longer than 80 cm)
>2. the number of cable is limited to one or maximum 2 cables.
>3. the frequencies produced in the equipment have to be low due the
>limitation of the method to 300 MHz.
>
>Reasons for
>1. the cable should be the preferred antenna for the emission of the device
>2. You can only made a correlation between CE and RE if all the radiated by
>the one cable. You will not be able to calculate the sum of different
cables
>because you don't know the relation.
>3. The method is only specified up to 300 MHz. At higher frequencies the
>cables act different.
>
>This method was used e. g. simple household devices and tools.
>
>I don't know if I got the real point because I didn't followed the whole
>discussion, but perhaps I can put in some more ideas.
>
>Best Regards
>
>Lothar Schmidt
>Technical Manager EMC/Bluetooth,
>BQB, Competent Body
>Cetecom Inc.
>411 Dixon Landing Road
>Milpitas, CA 95035
>Phone: +1 (408) 586 6214
>Fax: +1 (408) 586 6299
>
>
>-----Original Message-----
>From: Ken Javor [mailto:[email protected]]
>Sent: Tuesday, January 16, 2001 7:45 AM
>To: Ralph Cameron; chris maxwell; dan kwok
>Cc: EMC-PCST (E-mail)
>Subject: Re: Site Correlation
>
>
>
>I am getting the distinct (but uncomfortable) feeling that was is being
>discussed by a lot of people on this thread is that cable cm CE need to be
>controlled to prevent either crosstalk to another bundle, or to prevent
>interference to equipment connected to the same bundle. Am I interpreting
>these comments correctly? For the record, I don't believe either of these
>is a real issue. The only traditional, and in my experience, legitimate
>purpose of controlling cable cm CE is to prevent coupling to the antennas
>connected to radio receivers.
>
>Ken Javor
>
>----------
> >From: "Ralph Cameron" <[email protected]>
> >To: "Chris Maxwell" <[email protected]>, "Ken Javor"
><[email protected]>, "dan kwok" <[email protected]>
> >Cc: "EMC-PCST \(E-mail\)" <[email protected]>
> >Subject: Re: Site Correlation
> >Date: Tue, Jan 16, 2001, 9:01 AM
> >
>
> > What it boils down to Chris is the lack of immunity of the consumer
> > equipment contributes to degradation of the intended function. Once the
> > undesired energy reaches the consumer device there's no way to get rid
of
> > it. The rememdy is to prevent it from reaching the device and or
isolating
> > it from the source.
> >
> > At one time injection clamps were used for immunity testing- are they
>still?
> >
> > Ralph Cameron
> >
> >
> > ----- Original Message -----
> > From: "Chris Maxwell" <[email protected]>
> > To: "'Ralph Cameron'" <[email protected]>; "Ken Javor"
> > <[email protected]>; "dan kwok" <[email protected]>
> > Cc: "EMC-PCST (E-mail)" <[email protected]>
> > Sent: Tuesday, January 16, 2001 8:38 AM
> > Subject: RE: Site Correlation
> >
> >
> >> Seems like this thread has gotten into how to correlate common mode
cable
> >> currents with their expected radiated emissions.
> >>
> >> For those interested, Fischer Custom Communications makes coupling and
> >> measuring clamps which can measure common mode surface currents on
cables
> >> and surfaces. They used to publish some application notes regarding
the
> >> usage of their clamps to measure surface/cable currents and how to
> > correlate
> >> them to expected radiated emissions.
> >>
> >> I read them a couple of years ago. I never bought the clamps, but it
did
> >> make for some very good technical reading.
> >>
> >> I do know of a table top power supply manufacturer that uses this
method
> >> almost exclusively. They send one power supply to a calibrated OATS.
> > They
> >> get it to pass. Then, when the sample comes back to the factory, they
> > take
> >> clamp measurements of the common mode currents of the AC input and DC
> > output
> >> cable.
> >>
> >> They then model the power supply as a dipole antenna with the AC input
> > cable
> >> and DC output cable being the two poles.
> >>
> >> For future power supplies, they then use the clamp method in-house to
> >> measure the cable currents, if the currents pass, they assume the
supply
> >> passes radiated emissions.
> >>
> >> This won't work for every product, but it does fit this application
well.
> >> The power supply company could make more than 10 versions (3.3VDC,
5VDC,
> >> 9VDC, 12VDC ...) of a power supply with the same case and cabling so it
> > can
> >> save them a great deal of time and money. The supplies only have two
> >> cables, which is easy to model. The supplies have clock speeds in the
> >> 100-500Khz range, meaning that most of thier harmonics will be "dead"
>over
> >> 230Mhz, which is the cutoff for most coupling clamps.
> >>
> >> I thought that this method would be difficult to use for our products
> > since
> >> we have higher clock speeds and multiple cables.
> >>
> >> I guess many times the measurement method is somewhat defined by what
> > you're
> >> measuring.
> >>
> >> Chris Maxwell
> >> Design Engineer
> >> GN Nettest
> >> 6 Rhoads Drive, Building 4
> >> Utica,NY 13502
> >> email: [email protected]
> >> phone: 315-266-5128
> >> fax: 315-797-8024
> >>
> >>
> >>
> >>
> >> > -----Original Message-----
> >> > From: Ralph Cameron [SMTP:[email protected]]
> >> > Sent: Monday, January 15, 2001 10:57 PM
> >> > To: Ken Javor; dan kwok
> >> > Cc: EMC-PCST (E-mail)
> >> > Subject: Re: Site Correlation
> >> >
> >> >
> >> > No, your message is clear, what I am saying is that the emissions
below
> >> > 30Mhz cause the majority of the interference problems to consumer
> >> > electronics and that's not being addressed.
> >> >
> >> > Ralph Cameron
> >> >
> >> > ----- Original Message -----
> >> > From: "Ken Javor" <[email protected]>
> >> > To: "Ralph Cameron" <[email protected]>; "dan kwok" <[email protected]>
> >> > Cc: "EMC-PCST (E-mail)" <[email protected]>
> >> > Sent: Monday, January 15, 2001 10:34 PM
> >> > Subject: Re: Site Correlation
> >> >
> >> >
> >> > > I must have been unclear in my previous message. The purpose of
> >> > controlling
> >> > > cable cm CE is to control the resultant cable-induced RE, which are
> >> > > controlled to protect tunable antenna-connected radio receivers,
> > period.
> >> > > There was never any other purpose for controlling CE or RE.
> >> > >
> >> > > Ken Javor
> >> > >
> >> > > ----------
> >> > > >From: "Ralph Cameron" <[email protected]>
> >> > > >To: "Ken Javor" <[email protected]>, "Dan Kwok"
> >> > <[email protected]>
> >> > > >Cc: "EMC-PCST \(E-mail\)" <[email protected]>
> >> > > >Subject: Re: Site Correlation
> >> > > >Date: Mon, Jan 15, 2001, 8:51 PM
> >> > > >
> >> > >
> >> > > > Perhaps what you state is correct Ken but there has been a
> > supposition
> >> > that
> >> > > > RE , induced or other wise when converted to conducted current
does
> >> > not
> >> > > > effect other devices connected to those same conductors whether
>they
> >> > be
> >> > > > power, incoming TV or telephone cables etc. All these conductors
> >> > intercept
> >> > > > RE and their effects have been eliminated in 90% of cases( I
have
> >> > > > personally suppressed ) , by suppresseing the common mode
> > signals.Over
> >> > 300
> >> > > > successes is a significant statistic.
> >> > > >
> >> > > > Ralph Cameron
> >> > > >
> >> > > >
> >> > > > .
> >> > > > ----- Original Message -----
> >> > > > From: "Ken Javor" <[email protected]>
> >> > > > To: "Dan Kwok" <[email protected]>; "Ralph Cameron"
> > <[email protected]>
> >> > > > Cc: "EMC-PCST (E-mail)" <[email protected]>
> >> > > > Sent: Monday, January 15, 2001 5:42 PM
> >> > > > Subject: Re: Site Correlation
> >> > > >
> >> > > >
> >> > > >>
> >> > > >> Mr. Kwok's theories are logical and no doubt bear on the
subject,
> > but
> >> > > > there
> >> > > >> is a historical angle that bears inspection. About the time FCC
> >> > limits
> >> > > > for
> >> > > >> IT equipment were being drawn up (late '70s) PCs were not yet on
> >> > > > everyone's
> >> > > >> desktop. Most of the business equipment that would have been
> >> > envisioned
> >> > > > to
> >> > > >> be qualified to USC Title 47, Part 15, Subpart J would have been
> >> > > > stand-alone
> >> > > >> items such a copier, with the only cable connection being ac
>power.
> >> > The
> >> > > >> report which documents the development of the CE and RE
>limits/test
> >> > > > methods
> >> > > >> found in the above mentioned FCC limits specifically states that
>30
> >> > MHz
> >> > > > was
> >> > > >> picked as the cutoff between CE and RE for the reason of
radiation
> >> > > >> efficiency per Mr. Kwok's surmise, but also because 30 MHz was
the
> >> > lowest
> >> > > >> frequency at which a 3 m OATS measurement would provide the
>desired
> >> > > >> accuracy.
> >> > > >>
> >> > > >> Ken Javor
> >> > > >>
> >> > > >> P.S. Said report also demonstrated that the CE limit below 30
MHz
> >> > > > sufficed
> >> > > >> to control RE from the power cable to levels sufficient to
protect
> >> > against
> >> > > >> cable radiation-induced rfi.
> >> > > >>
> >> > > >> ----------
> >> > > >> >From: Dan Kwok <[email protected]>
> >> > > >> >To: Ralph Cameron <[email protected]>
> >> > > >> >Cc: "EMC-PCST (E-mail)" <[email protected]>
> >> > > >> >Subject: Re: Site Correlation
> >> > > >> >Date: Mon, Jan 15, 2001, 2:49 PM
> >> > > >> >
> >> > > >>
> >> > > >> >
> >> > > >> > Hello Ralph:
> >> > > >> >
> >> > > >> > That's a good question. At one time, I pondered the same
>question
> >> > > >> > myself. There are obviously plenty of communication systems
> >> > operating
> >> > > >> > under 30 MHz. I suppose there are reasons why CISPR or CISPR
22
> >> > does
> >> > not
> >> > > >> > specify radiated emissions below 30 MHz. I can suggest one
> >> > possibility.
> >> > > >> > Perhaps others here will come up with more.
> >> > > >> >
> >> > > >> > For a fixed cable of length L, the ratio of L/lambda gets
> >> > progressively
> >> > > >> > small for frequencies much less than 30 MHz with most
commercial
> >> > EUTs.
> >> > > >> > If we consider the cable part of dipole antenna, the reduction
>in
> >> > > >> > frequency has a diminishing effect on the antenna's radiation
> >> > > >> > resistance. Given a constant current, the radiated power would
> >> > decrease
> >> > > >> > with decreasing radiation resistance. At 550 KHz (bottom of
the
> > AM
> >> > > >> > broadcast band in North America), the 1/4 wavelength is 136
> > meters.
> >> > Even
> >> > > >> > if the antenna's reactance is ignored, one would need very
long
> >> > cables
> >> > > >> > driven by a significant CM noise voltage at this frequency to
> >> > radiate
> >> > > >> > much energy.
> >> > > >> >
> >> > > >> > --
> >> > > >>
> >> >
> >>
------------------------------------------------------------------------
> >> > > >> > Daniel Kwok
> >> > > >> > Principal EMC Engineer
> >> > > >> > Intetron Consulting, Inc.
> >> > > >> > Vancouver, Canada
> >> > > >> > Phone (604) 432-9874
> >> > > >> > Email [email protected]
> >> > > >> > Web http://www.intetron.com";
> >> > > >> >
> >> > > >> >
> >> > > >> > Ralph Cameron wrote:
> >> > > >> >>
> >> > > >> >> Ken:
> >> > > >> >>
> >> > > >> >> I like the idea of setting a limit to common mode currents on
> >> > attaching
> >> > > >> >> cables but mI wonder why CISPR has chosen to start such
> >> > measurements
> >> > at
> >> > > >> >> 30Mhz when most of the common mode currents are the result of
> >> > switching
> >> > > >> >> products and are generated harmonically from the fundamental
> > and
> >> > as
> >> > > > such
> >> > > >> >> propagate from the low Khz range up through 30Mhz. is there
no
> >> > > > consideration
> >> > > >> >> for those who occupy the spectrum below 30Mhz?
> >> > > >> >>
> >> > > >> >
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