Hello Dan: Your explanation makes a lot of sense, as applied to RE. It appears that conducted emissions or CE have been largely ignored' nevertheless, cause many problems when the radiating source is external to the device. The average home is a great "unintentionl " antenna and when conducted currents from noisey switching power supplies or RF from local transmitting facilities, etc appear on house wiring it causes two problems: It radiates ( or re readiates, as the case may be) and disupts or causes radiosensitive equipment to malfuntion or as they say, " respond in an unintended manner". This issue has not been addressed very well, except equipment bearing the CE mark does have some conducted immunity , so it is a feature that has a benefit in spite of how some have defined the CE mark.
My reason for asking about the frequency range of the RE measurements was to determine the background behind the restriction in the frequency range. It also related to the incidence of equipment malfucntion being almost entirely due to common mode conducted currents. Of course, once RE are intercepted by house wiring they become conducted and that's when the problem begins. You answerd the original question , thanks. Ralph Cameron EMC Consulting and Suppression of Consumer Elecrtonic Equipment ( After sale) p.s. After sale means that only common mode suppression techniques are used to suppress line conducted currents. This does not effect warranty or electrical safety in any way. ----- Original Message ----- From: "Dan Kwok" <[email protected]> To: "Ralph Cameron" <[email protected]> Cc: "EMC-PCST (E-mail)" <[email protected]> Sent: Monday, January 15, 2001 3:49 PM Subject: Re: Site Correlation > 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]
