Actually since you mention it my application for cable cm CE control covered the spectrum from 150 kHz to 200 MHz! But the application was aerospace-related. I have to say, however that I think an I/O cable would be driven by PCB ground noise, which would be clock-speed related, not power supply switching-speed related.
Ken Javor ---------- ---------- >From: "Ralph Cameron" <[email protected]> >To: "Ken Javor" <[email protected]>, "David Heald" <[email protected]>, "Tudor, Allen" <[email protected]> >Cc: "EMC-PCST \(E-mail\)" <[email protected]> >Subject: Re: Site Correlation >Date: Sun, Jan 14, 2001, 7:57 AM > > 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? > > In my applications of common mode suppression, almost every case, the source > generating the common mode currents , when suppressed with simple external > common mode chokes, satisfactorily reduced all the localized radiation > caused by such effects. > > Series common mode chokes not only suppress the outgoing but reduce the > incoming common mode currents that have the same potential for casuing > equipment malfunction. > > > Ralph Cameron > EMC Consulting and Suppression of Consumer Electronic Equipment > (After Sale). > > ----- Original Message ----- > From: "Ken Javor" <[email protected]> > To: "David Heald" <[email protected]>; "Tudor, Allen" > <[email protected]> > Cc: "EMC-PCST (E-mail)" <[email protected]> > Sent: Saturday, January 13, 2001 3:43 AM > Subject: Re: Site Correlation > > >> >> I must say that this thread has been a refreshing alternative to the >> EMC-law/regulations questions that typically occupy this service. Not >> complaining either, because If I suddenly found myself working commercial >> EMC issues I would likely be flooding this line with those self-same >> questions. >> >> Almost as an aside, Mr. Heald raises an issue of enduring interest to > myself >> and others. >> >> "Another important factor... is to manipulate the cables during testing > (oh, >> how much easier our job would be without cables)." >> >> The same issue was raised parenthetically in my answer to the question > about >> GTEM polarization. The issue is control of cable-sourced radiated >> emissions. I am now about to allegorically take a baseball bat to a >> hornets' nest... >> >> Bela Szentkuti pointed out almost twenty years ago that it would be much >> more efficient and accurate to analytically/experimentally determine the >> relationship between cable common mode currents and the resultant radiated >> field based on the maximum possible radiation efficiency of that cable, > and >> use that relationship to derive a common mode current limit for cables > from >> 30 MHz to 1 GHz, using the absorbing clamp as a measuring tool. This > would >> speed up OATS or any other kind of RE testing by deleting the requirement > to >> maximize cable radiation. >> >> So this question is a poll. How do the subscribers to this service feel >> about cable common mode current control in lieu of direct measurement of >> cable-sourced RE measurement? The idea being that first you would measure >> and bring cable cm CE into compliance with a cable-type limit and only > then >> would you make the RE measurement. The cables would only be support >> equipment which did not contribute to the RE profile, hence any measured >> emissions at or near the limit would be guaranteed EUT enclosure-related. >> >> Polite responses only, please!!! >> >> Ken Javor >> >> >> >> ---------- >> >From: David Heald <[email protected]> >> >To: "Tudor, Allen" <[email protected]> >> >Cc: "EMC-PCST (E-mail)" <[email protected]> >> >Subject: Re: Site Correlation >> >Date: Fri, Jan 12, 2001, 9:36 AM >> > >> >> > >> > Greetings again. >> > I received some questions about this off list and there has been more >> > discussion in this direction, so I thought I would throw my other two >> > cents in. >> > For small fully anechoic chambers with little room for antenna height >> > adjustment, you should be able to have uncertainty of about 6dB or so >> > (10dB is much safer realistically) when you apply correction factors for >> > a 10m site. The reason for this is, as John Barnes pointed out, the >> > absence of reflected waves being received in addition to the direct >> > waves. The key importance to a fully lined chamber (including the >> > floor) is that destructive waves are not present. With a reflective >> > floor, destructive waves can lower your readings by more than 30dB. Add >> > this to the 6 dB or so of uncertainty for additive waves and your total >> > error could be enormous. With an absorber lined floor, the influence of >> > the destructive waves is eliminated or reduced, so a correlation of 6dB >> > (again 10dB is safer) should be achievable (this simply accounts for the >> > absence of constructive interference). >> > Another important factor to ensure you don't have any surprises when >> > moving from precompliance to a compliance run is to manipulate the >> > cables during testing (oh, how much easier our job would be without >> > cables). Large signal strength changes can be achieved just by moving >> > cables a few inches. >> > I also have to agree with Gert's and Ken's comments on far field >> > measurements. I mentioned this in my original message, but didn't >> > elaborate at all. These are very important considerations that can >> > greatly affect any expected correlation to a 10m OATS. >> > >> > -- >> > David Heald >> > Senior EMC Engineer/ >> > Product Safety Engineer >> > >> > Curtis-Straus LLC NRTL >> > Laboratory for NEBS, EMC, Safety, and Telecom >> > Voice:978.486.8880x254 Fax:978.486.8828 >> > www.curtis-straus.com >> > >> > >> > Tudor, Allen wrote: >> > >> >> Greetings: >> >> >> >> What's the best way to correlate a pre-compliance chamber (smaller than > a 3m >> >> chamber) to a 10m anechoic chamber? Should I use a signal generator > and >> >> antenna or should I use a comb generator? >> >> >> >> Would the answer be different if I were correlating the pre-compliance >> >> chamber to an OATS? >> >> >> >> Thanks in advance. >> >> >> >> >> >> Allen Tudor, Compliance Engineer >> >> ADC DSL Systems Inc. >> >> 6531 Meridien Dr. >> >> Raleigh, NC 27616 >> >> phone: 919.875.3382 >> >> email: [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] >> > >> > >> >> ------------------------------------------- >> 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]
