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? > >> > > > > ------------------------------------------- > > This message is from the IEEE EMC Society Product Safety > > Technical Committee emc-pstc discussion list. > > > > To cancel your subscription, send mail to: > > [email protected] > > with the single line: > > unsubscribe emc-pstc > > > > For help, send mail to the list administrators: > > Jim Bacher: [email protected] > > Michael Garretson: [email protected] > > > > For policy questions, send mail to: > > Richard Nute: [email protected] > > > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > > > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
