I think you misunderstood a couple of my arguments. A CE limit on cables would not pre-empt the RE test, it would simply remove the cables as radiation sources, thereby eliminating the need to arrange them for maximum radiation. A cable CE limit would be based on an ideal maximum radiation orientation, therefore in practice measured radiation from a CE compliant cable would always be below the RE limit.
The size of the EUT would not play a role, since you would always perform the RE test. And finally, I specifically talked about the absorber clamp because it damps out standing waves - the only issue, as Ing. Gremmen pointed out earlier, is how close can you get the clamp to the EUT - it must be within a small fraction of a wavelength - say 0.1 lambda. Ken Javor ---------- >From: Cortland Richmond <[email protected]> >To: "Ken Javor" <[email protected]>, ieee pstc list <[email protected]> >Subject: Re: Site Correlation >Date: Sat, Jan 13, 2001, 5:34 PM > > Ken, > > When you ask how members "feel," you open a Pandora's box! > > We must still meet some kind of installed bottom line; our equipment must > not generate fields above some limit. (We can argue what that should be > some other time.) > > However, when _designing_ an EMC solution, we can estimate field strength > based on some arbitrary gain, current and impedance for cables. By assuming > all common-mode currents flow in the worst possible directions -- here's > our cable arrangement -- we come up with a conservative solution. > > But cables coming from a (say) two-meter square EUT cannot take all > possible configurations. GR-1089 assumes a limited cable arrangement > representative of a Central Office installation. And when an EUT gets large > enough, it's no longer enough to know what current flows in the cables > anyway, because the EUT may be a principal radiator by itself. > > So I'd not want all radiated tests replaced. We sill need a size limit to > tell when we must use antennas, and when current probes. We also need a > more flexible definition how and where cable current is to be measured. Not > al cables can be run along the floor on a reasonable test site. If we must > reach a current maximum with a probe, we may have to get five meters from > the EUT. That might require a ten meter diameter ground plane -- which > brings to mind the saying: Be careful what you ask for; you might get it! > > Regards, > > Cortland > > (Whose posting here reflect none of his employer's opinions) > > > > ====================== Original Message Follows ==================== > > >> Date: 13-Jan-01 00:50:16 MsgID: 1077-20414 ToID: 72146,373 > From: "Ken Javor" >INTERNET:[email protected] > Subj: Re: Site Correlation > Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 > > Date: Sat, 13 Jan 2001 02:43:51 -0600 > Subject: Re: Site Correlation > From: "Ken Javor" <[email protected]> > Reply-To: "Ken Javor" <[email protected]> > > > 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] > > ====================== End of Original Message ===================== > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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