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? >> >> >> > >> > ------------------------------------------- >> > 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. 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