RE: Site Correlation
Paolo, Actually, we did give a damn about you. If you just follow for a couple of paragraphs, maybe you'll see how. One of the problems with small pre-compliance chambers is that it is sometimes hard if not impossible to fit the DUT and all of its associated cabling into the chamber. Also, even if you can fit the cables, it may be hard for a small chamber to measure the cable emissions accurately. We use a 0.7m cubic G-Strip (not a G-TEM) cell for pre-compliance emissions measurements and A-B comparisons. The chamber is fully anechoic, so reflections aren't a problem. However, cables are a problem. Usually, what I end up doing is: After we finish pre-compliance, I take a product to the OATS for compliance testing. I bring the product back to our lab and put it in our chamber. However, in order to fit it in, I usually have to strip the serial cable, keyboard, mouse, parallel cable and VGA cable. All that I can fit in the chamber is the unit and the power supply. I then take a reference measurement of this stripped system. I store these readings for future A-B comparisons. When I do these A-B comparisons, it would be nice to supplement them with coupling clamp measurements from the cables before I remove them. I would then possibly have a more complete picture by using the small cell to assess the enclosure radiation and the coupling clamps to assess the cable radiation. I believe that this is how the CE vs. RE measurement methods for cables got mixed into the thread. Using a combination of small chambers for the enclosure emissions and clamp measurements for the cable emissions may provide a more complete picture than using the chamber alone. This may have been where Ken Javor was going when he brought up the possibility of measuring cable emissions with a clamp. I personally don't know of anybody performing this combination measurement. It sounds like a good idea, but it would be nice to hear if anyone has real life experience with it. It may add some useful information to the original question that started this thread, which was how well small chamber emissions measurements correlate with OATS measurements. Chris Maxwell Design Engineer GN Nettest 6 Rhoads Drive, Building 4 Utica,NY 13502 email: chris.maxw...@gnnettest.com phone: 315-266-5128 fax: 315-797-8024 -Original Message- From: Paolo Roncone [SMTP:paolo...@tin.it] Sent: Wednesday, January 17, 2001 6:08 AM To: Lothar Schmidt Cc: EMC-PCST (E-mail) Subject: RE: Site Correlation Good point Lothar, it was about time that the original technical grounds and limitations of CE method were brought up. Just one additional point: with the ever increasing operating frequencies of many electronic products, box and/or PCB level radiation is getting more and more important vs cable radiation (and as a by-product cable layout should weigh less in measurement uncertainty). One last point: I was a bit perplexed by the way this thread shifted from the original question. I myself stepped in early with a question about fully-anechoic vs semi-anechoic pre-compliance chambers but then the subject switched to the CE vs RE issue and nobody gave a damn about me.. Paolo At 11:28 AM 1/16/01 -0800, Lothar Schmidt wrote: I have the feeling that different issues are mixed in this discussion. supposed that CE vs. RE methods is the issue, I can give you some historical information. The CE method is used as a simplified method for the radiation of the tested device. The CE method was used for devices which have to met several conditions 1. the cable length was long compared to the size of the device ( the longest side should not be longer than 80 cm) 2. the number of cable is limited to one or maximum 2 cables. 3. the frequencies produced in the equipment have to be low due the limitation of the method to 300 MHz. Reasons for 1. the cable should be the preferred antenna for the emission of the device 2. You can only made a correlation between CE and RE if all the radiated by the one cable. You will not be able to calculate the sum of different cables because you don't know the relation. 3. The method is only specified up to 300 MHz. At higher frequencies the cables act different. This method was used e. g. simple household devices and tools. I don't know if I got the real point because I didn't followed the whole discussion, but perhaps I can put in some more ideas. Best Regards Lothar Schmidt Technical Manager EMC/Bluetooth, BQB, Competent Body Cetecom Inc. 411 Dixon Landing Road Milpitas, CA 95035 Phone: +1 (408) 586 6214 Fax: +1 (408) 586 6299 -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Tuesday, January 16, 2001 7:45 AM To: Ralph Cameron; chris maxwell; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I am getting the distinct (but uncomfortable) feeling
RE: Site Correlation
Many a good conversation veers off onto other interesting threads and indeed this is one of the things I enjoy about reading the various messages even those that have no direct impact on me. Sorry you felt ignored, although as I followed it the first responses did address the issue. It sorta can't be done, but you might want to try CE emissions as a way to correlate from your site data to the OATS 10 meter. Not trying to get your hackles up, but I would hate to see good discussions get stymied just because they wander from topic to topic. Take care Gary -Original Message- From: Paolo Roncone [mailto:paolo...@tin.it] Sent: Wednesday, January 17, 2001 3:08 AM To: Lothar Schmidt Cc: EMC-PCST (E-mail) Subject: RE: Site Correlation Good point Lothar, it was about time that the original technical grounds and limitations of CE method were brought up. Just one additional point: with the ever increasing operating frequencies of many electronic products, box and/or PCB level radiation is getting more and more important vs cable radiation (and as a by-product cable layout should weigh less in measurement uncertainty). One last point: I was a bit perplexed by the way this thread shifted from the original question. I myself stepped in early with a question about fully-anechoic vs semi-anechoic pre-compliance chambers but then the subject switched to the CE vs RE issue and nobody gave a damn about me.. Paolo At 11:28 AM 1/16/01 -0800, Lothar Schmidt wrote: I have the feeling that different issues are mixed in this discussion. supposed that CE vs. RE methods is the issue, I can give you some historical information. The CE method is used as a simplified method for the radiation of the tested device. The CE method was used for devices which have to met several conditions 1. the cable length was long compared to the size of the device ( the longest side should not be longer than 80 cm) 2. the number of cable is limited to one or maximum 2 cables. 3. the frequencies produced in the equipment have to be low due the limitation of the method to 300 MHz. Reasons for 1. the cable should be the preferred antenna for the emission of the device 2. You can only made a correlation between CE and RE if all the radiated by the one cable. You will not be able to calculate the sum of different cables because you don't know the relation. 3. The method is only specified up to 300 MHz. At higher frequencies the cables act different. This method was used e. g. simple household devices and tools. I don't know if I got the real point because I didn't followed the whole discussion, but perhaps I can put in some more ideas. Best Regards Lothar Schmidt Technical Manager EMC/Bluetooth, BQB, Competent Body Cetecom Inc. 411 Dixon Landing Road Milpitas, CA 95035 Phone: +1 (408) 586 6214 Fax: +1 (408) 586 6299 -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Tuesday, January 16, 2001 7:45 AM To: Ralph Cameron; chris maxwell; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I am getting the distinct (but uncomfortable) feeling that was is being discussed by a lot of people on this thread is that cable cm CE need to be controlled to prevent either crosstalk to another bundle, or to prevent interference to equipment connected to the same bundle. Am I interpreting these comments correctly? For the record, I don't believe either of these is a real issue. The only traditional, and in my experience, legitimate purpose of controlling cable cm CE is to prevent coupling to the antennas connected to radio receivers. Ken Javor -- From: Ralph Cameron ral...@igs.net To: Chris Maxwell chris.maxw...@gnnettest.com, Ken Javor ken.ja...@emccompliance.com, dan kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: Re: Site Correlation Date: Tue, Jan 16, 2001, 9:01 AM What it boils down to Chris is the lack of immunity of the consumer equipment contributes to degradation of the intended function. Once the undesired energy reaches the consumer device there's no way to get rid of it. The rememdy is to prevent it from reaching the device and or isolating it from the source. At one time injection clamps were used for immunity testing- are they still? Ralph Cameron - Original Message - From: Chris Maxwell chris.maxw...@gnnettest.com To: 'Ralph Cameron' ral...@igs.net; Ken Javor ken.ja...@emccompliance.com; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Tuesday, January 16, 2001 8:38 AM Subject: RE: Site Correlation Seems like this thread has gotten into how to correlate common mode cable currents with their expected radiated emissions. For those interested, Fischer Custom Communications makes coupling and measuring clamps which can measure common mode surface currents on cables and surfaces. They used
RE: Site Correlation
Good point Lothar, it was about time that the original technical grounds and limitations of CE method were brought up. Just one additional point: with the ever increasing operating frequencies of many electronic products, box and/or PCB level radiation is getting more and more important vs cable radiation (and as a by-product cable layout should weigh less in measurement uncertainty). One last point: I was a bit perplexed by the way this thread shifted from the original question. I myself stepped in early with a question about fully-anechoic vs semi-anechoic pre-compliance chambers but then the subject switched to the CE vs RE issue and nobody gave a damn about me.. Paolo At 11:28 AM 1/16/01 -0800, Lothar Schmidt wrote: I have the feeling that different issues are mixed in this discussion. supposed that CE vs. RE methods is the issue, I can give you some historical information. The CE method is used as a simplified method for the radiation of the tested device. The CE method was used for devices which have to met several conditions 1. the cable length was long compared to the size of the device ( the longest side should not be longer than 80 cm) 2. the number of cable is limited to one or maximum 2 cables. 3. the frequencies produced in the equipment have to be low due the limitation of the method to 300 MHz. Reasons for 1. the cable should be the preferred antenna for the emission of the device 2. You can only made a correlation between CE and RE if all the radiated by the one cable. You will not be able to calculate the sum of different cables because you don't know the relation. 3. The method is only specified up to 300 MHz. At higher frequencies the cables act different. This method was used e. g. simple household devices and tools. I don't know if I got the real point because I didn't followed the whole discussion, but perhaps I can put in some more ideas. Best Regards Lothar Schmidt Technical Manager EMC/Bluetooth, BQB, Competent Body Cetecom Inc. 411 Dixon Landing Road Milpitas, CA 95035 Phone: +1 (408) 586 6214 Fax: +1 (408) 586 6299 -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Tuesday, January 16, 2001 7:45 AM To: Ralph Cameron; chris maxwell; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I am getting the distinct (but uncomfortable) feeling that was is being discussed by a lot of people on this thread is that cable cm CE need to be controlled to prevent either crosstalk to another bundle, or to prevent interference to equipment connected to the same bundle. Am I interpreting these comments correctly? For the record, I don't believe either of these is a real issue. The only traditional, and in my experience, legitimate purpose of controlling cable cm CE is to prevent coupling to the antennas connected to radio receivers. Ken Javor -- From: Ralph Cameron ral...@igs.net To: Chris Maxwell chris.maxw...@gnnettest.com, Ken Javor ken.ja...@emccompliance.com, dan kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: Re: Site Correlation Date: Tue, Jan 16, 2001, 9:01 AM What it boils down to Chris is the lack of immunity of the consumer equipment contributes to degradation of the intended function. Once the undesired energy reaches the consumer device there's no way to get rid of it. The rememdy is to prevent it from reaching the device and or isolating it from the source. At one time injection clamps were used for immunity testing- are they still? Ralph Cameron - Original Message - From: Chris Maxwell chris.maxw...@gnnettest.com To: 'Ralph Cameron' ral...@igs.net; Ken Javor ken.ja...@emccompliance.com; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Tuesday, January 16, 2001 8:38 AM Subject: RE: Site Correlation Seems like this thread has gotten into how to correlate common mode cable currents with their expected radiated emissions. For those interested, Fischer Custom Communications makes coupling and measuring clamps which can measure common mode surface currents on cables and surfaces. They used to publish some application notes regarding the usage of their clamps to measure surface/cable currents and how to correlate them to expected radiated emissions. I read them a couple of years ago. I never bought the clamps, but it did make for some very good technical reading. I do know of a table top power supply manufacturer that uses this method almost exclusively. They send one power supply to a calibrated OATS. They get it to pass. Then, when the sample comes back to the factory, they take clamp measurements of the common mode currents of the AC input and DC output cable. They then model the power supply as a dipole antenna with the AC input cable and DC output cable being the two poles. For future power supplies, they then use the clamp method in-house to measure the cable
RE: Site Correlation
I have the feeling that different issues are mixed in this discussion. supposed that CE vs. RE methods is the issue, I can give you some historical information. The CE method is used as a simplified method for the radiation of the tested device. The CE method was used for devices which have to met several conditions 1. the cable length was long compared to the size of the device ( the longest side should not be longer than 80 cm) 2. the number of cable is limited to one or maximum 2 cables. 3. the frequencies produced in the equipment have to be low due the limitation of the method to 300 MHz. Reasons for 1. the cable should be the preferred antenna for the emission of the device 2. You can only made a correlation between CE and RE if all the radiated by the one cable. You will not be able to calculate the sum of different cables because you don't know the relation. 3. The method is only specified up to 300 MHz. At higher frequencies the cables act different. This method was used e. g. simple household devices and tools. I don't know if I got the real point because I didn't followed the whole discussion, but perhaps I can put in some more ideas. Best Regards Lothar Schmidt Technical Manager EMC/Bluetooth, BQB, Competent Body Cetecom Inc. 411 Dixon Landing Road Milpitas, CA 95035 Phone: +1 (408) 586 6214 Fax: +1 (408) 586 6299 -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Tuesday, January 16, 2001 7:45 AM To: Ralph Cameron; chris maxwell; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I am getting the distinct (but uncomfortable) feeling that was is being discussed by a lot of people on this thread is that cable cm CE need to be controlled to prevent either crosstalk to another bundle, or to prevent interference to equipment connected to the same bundle. Am I interpreting these comments correctly? For the record, I don't believe either of these is a real issue. The only traditional, and in my experience, legitimate purpose of controlling cable cm CE is to prevent coupling to the antennas connected to radio receivers. Ken Javor -- From: Ralph Cameron ral...@igs.net To: Chris Maxwell chris.maxw...@gnnettest.com, Ken Javor ken.ja...@emccompliance.com, dan kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: Re: Site Correlation Date: Tue, Jan 16, 2001, 9:01 AM What it boils down to Chris is the lack of immunity of the consumer equipment contributes to degradation of the intended function. Once the undesired energy reaches the consumer device there's no way to get rid of it. The rememdy is to prevent it from reaching the device and or isolating it from the source. At one time injection clamps were used for immunity testing- are they still? Ralph Cameron - Original Message - From: Chris Maxwell chris.maxw...@gnnettest.com To: 'Ralph Cameron' ral...@igs.net; Ken Javor ken.ja...@emccompliance.com; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Tuesday, January 16, 2001 8:38 AM Subject: RE: Site Correlation Seems like this thread has gotten into how to correlate common mode cable currents with their expected radiated emissions. For those interested, Fischer Custom Communications makes coupling and measuring clamps which can measure common mode surface currents on cables and surfaces. They used to publish some application notes regarding the usage of their clamps to measure surface/cable currents and how to correlate them to expected radiated emissions. I read them a couple of years ago. I never bought the clamps, but it did make for some very good technical reading. I do know of a table top power supply manufacturer that uses this method almost exclusively. They send one power supply to a calibrated OATS. They get it to pass. Then, when the sample comes back to the factory, they take clamp measurements of the common mode currents of the AC input and DC output cable. They then model the power supply as a dipole antenna with the AC input cable and DC output cable being the two poles. For future power supplies, they then use the clamp method in-house to measure the cable currents, if the currents pass, they assume the supply passes radiated emissions. This won't work for every product, but it does fit this application well. The power supply company could make more than 10 versions (3.3VDC, 5VDC, 9VDC, 12VDC ...) of a power supply with the same case and cabling so it can save them a great deal of time and money. The supplies only have two cables, which is easy to model. The supplies have clock speeds in the 100-500Khz range, meaning that most of thier harmonics will be dead over 230Mhz, which is the cutoff for most coupling clamps. I thought that this method would be difficult to use for our products since we have higher clock speeds and multiple cables. I guess many times the measurement
Re: Site Correlation
I am getting the distinct (but uncomfortable) feeling that was is being discussed by a lot of people on this thread is that cable cm CE need to be controlled to prevent either crosstalk to another bundle, or to prevent interference to equipment connected to the same bundle. Am I interpreting these comments correctly? For the record, I don't believe either of these is a real issue. The only traditional, and in my experience, legitimate purpose of controlling cable cm CE is to prevent coupling to the antennas connected to radio receivers. Ken Javor -- From: Ralph Cameron ral...@igs.net To: Chris Maxwell chris.maxw...@gnnettest.com, Ken Javor ken.ja...@emccompliance.com, dan kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: Re: Site Correlation Date: Tue, Jan 16, 2001, 9:01 AM What it boils down to Chris is the lack of immunity of the consumer equipment contributes to degradation of the intended function. Once the undesired energy reaches the consumer device there's no way to get rid of it. The rememdy is to prevent it from reaching the device and or isolating it from the source. At one time injection clamps were used for immunity testing- are they still? Ralph Cameron - Original Message - From: Chris Maxwell chris.maxw...@gnnettest.com To: 'Ralph Cameron' ral...@igs.net; Ken Javor ken.ja...@emccompliance.com; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Tuesday, January 16, 2001 8:38 AM Subject: RE: Site Correlation Seems like this thread has gotten into how to correlate common mode cable currents with their expected radiated emissions. For those interested, Fischer Custom Communications makes coupling and measuring clamps which can measure common mode surface currents on cables and surfaces. They used to publish some application notes regarding the usage of their clamps to measure surface/cable currents and how to correlate them to expected radiated emissions. I read them a couple of years ago. I never bought the clamps, but it did make for some very good technical reading. I do know of a table top power supply manufacturer that uses this method almost exclusively. They send one power supply to a calibrated OATS. They get it to pass. Then, when the sample comes back to the factory, they take clamp measurements of the common mode currents of the AC input and DC output cable. They then model the power supply as a dipole antenna with the AC input cable and DC output cable being the two poles. For future power supplies, they then use the clamp method in-house to measure the cable currents, if the currents pass, they assume the supply passes radiated emissions. This won't work for every product, but it does fit this application well. The power supply company could make more than 10 versions (3.3VDC, 5VDC, 9VDC, 12VDC ...) of a power supply with the same case and cabling so it can save them a great deal of time and money. The supplies only have two cables, which is easy to model. The supplies have clock speeds in the 100-500Khz range, meaning that most of thier harmonics will be dead over 230Mhz, which is the cutoff for most coupling clamps. I thought that this method would be difficult to use for our products since we have higher clock speeds and multiple cables. I guess many times the measurement method is somewhat defined by what you're measuring. Chris Maxwell Design Engineer GN Nettest 6 Rhoads Drive, Building 4 Utica,NY 13502 email: chris.maxw...@gnnettest.com phone: 315-266-5128 fax: 315-797-8024 -Original Message- From: Ralph Cameron [SMTP:ral...@igs.net] Sent: Monday, January 15, 2001 10:57 PM To: Ken Javor; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation No, your message is clear, what I am saying is that the emissions below 30Mhz cause the majority of the interference problems to consumer electronics and that's not being addressed. Ralph Cameron - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: Ralph Cameron ral...@igs.net; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Monday, January 15, 2001 10:34 PM Subject: Re: Site Correlation 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 ral...@igs.net To: Ken Javor ken.ja...@emccompliance.com, Dan Kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org 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
Re: Site Correlation
In a message dated 1/16/01 7:09:38 AM Pacific Standard Time, ral...@igs.net writes: What it boils down to Chris is the lack of immunity of the consumer equipment contributes to degradation of the intended function. Ralph, I've made this point to Art Wall of the FCC many times, he does not want to enforce immunity in the USA. I think that this is a mistake, considdering most companies are doing for Europe anyway. Derek. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
What it boils down to Chris is the lack of immunity of the consumer equipment contributes to degradation of the intended function. Once the undesired energy reaches the consumer device there's no way to get rid of it. The rememdy is to prevent it from reaching the device and or isolating it from the source. At one time injection clamps were used for immunity testing- are they still? Ralph Cameron - Original Message - From: Chris Maxwell chris.maxw...@gnnettest.com To: 'Ralph Cameron' ral...@igs.net; Ken Javor ken.ja...@emccompliance.com; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Tuesday, January 16, 2001 8:38 AM Subject: RE: Site Correlation Seems like this thread has gotten into how to correlate common mode cable currents with their expected radiated emissions. For those interested, Fischer Custom Communications makes coupling and measuring clamps which can measure common mode surface currents on cables and surfaces. They used to publish some application notes regarding the usage of their clamps to measure surface/cable currents and how to correlate them to expected radiated emissions. I read them a couple of years ago. I never bought the clamps, but it did make for some very good technical reading. I do know of a table top power supply manufacturer that uses this method almost exclusively. They send one power supply to a calibrated OATS. They get it to pass. Then, when the sample comes back to the factory, they take clamp measurements of the common mode currents of the AC input and DC output cable. They then model the power supply as a dipole antenna with the AC input cable and DC output cable being the two poles. For future power supplies, they then use the clamp method in-house to measure the cable currents, if the currents pass, they assume the supply passes radiated emissions. This won't work for every product, but it does fit this application well. The power supply company could make more than 10 versions (3.3VDC, 5VDC, 9VDC, 12VDC ...) of a power supply with the same case and cabling so it can save them a great deal of time and money. The supplies only have two cables, which is easy to model. The supplies have clock speeds in the 100-500Khz range, meaning that most of thier harmonics will be dead over 230Mhz, which is the cutoff for most coupling clamps. I thought that this method would be difficult to use for our products since we have higher clock speeds and multiple cables. I guess many times the measurement method is somewhat defined by what you're measuring. Chris Maxwell Design Engineer GN Nettest 6 Rhoads Drive, Building 4 Utica,NY 13502 email: chris.maxw...@gnnettest.com phone: 315-266-5128 fax: 315-797-8024 -Original Message- From: Ralph Cameron [SMTP:ral...@igs.net] Sent: Monday, January 15, 2001 10:57 PM To: Ken Javor; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation No, your message is clear, what I am saying is that the emissions below 30Mhz cause the majority of the interference problems to consumer electronics and that's not being addressed. Ralph Cameron - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: Ralph Cameron ral...@igs.net; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Monday, January 15, 2001 10:34 PM Subject: Re: Site Correlation 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 ral...@igs.net To: Ken Javor ken.ja...@emccompliance.com, Dan Kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org 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 ken.ja...@emccompliance.com To: Dan Kwok dk...@intetron.com; Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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
RE: Site Correlation
Seems like this thread has gotten into how to correlate common mode cable currents with their expected radiated emissions. For those interested, Fischer Custom Communications makes coupling and measuring clamps which can measure common mode surface currents on cables and surfaces. They used to publish some application notes regarding the usage of their clamps to measure surface/cable currents and how to correlate them to expected radiated emissions. I read them a couple of years ago. I never bought the clamps, but it did make for some very good technical reading. I do know of a table top power supply manufacturer that uses this method almost exclusively. They send one power supply to a calibrated OATS. They get it to pass. Then, when the sample comes back to the factory, they take clamp measurements of the common mode currents of the AC input and DC output cable. They then model the power supply as a dipole antenna with the AC input cable and DC output cable being the two poles. For future power supplies, they then use the clamp method in-house to measure the cable currents, if the currents pass, they assume the supply passes radiated emissions. This won't work for every product, but it does fit this application well. The power supply company could make more than 10 versions (3.3VDC, 5VDC, 9VDC, 12VDC ...) of a power supply with the same case and cabling so it can save them a great deal of time and money. The supplies only have two cables, which is easy to model. The supplies have clock speeds in the 100-500Khz range, meaning that most of thier harmonics will be dead over 230Mhz, which is the cutoff for most coupling clamps. I thought that this method would be difficult to use for our products since we have higher clock speeds and multiple cables. I guess many times the measurement method is somewhat defined by what you're measuring. Chris Maxwell Design Engineer GN Nettest 6 Rhoads Drive, Building 4 Utica,NY 13502 email: chris.maxw...@gnnettest.com phone: 315-266-5128 fax: 315-797-8024 -Original Message- From: Ralph Cameron [SMTP:ral...@igs.net] Sent: Monday, January 15, 2001 10:57 PM To: Ken Javor; dan kwok Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation No, your message is clear, what I am saying is that the emissions below 30Mhz cause the majority of the interference problems to consumer electronics and that's not being addressed. Ralph Cameron - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: Ralph Cameron ral...@igs.net; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Monday, January 15, 2001 10:34 PM Subject: Re: Site Correlation 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 ral...@igs.net To: Ken Javor ken.ja...@emccompliance.com, Dan Kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org 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 ken.ja...@emccompliance.com To: Dan Kwok dk...@intetron.com; Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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
Re: Site Correlation
No, your message is clear, what I am saying is that the emissions below 30Mhz cause the majority of the interference problems to consumer electronics and that's not being addressed. Ralph Cameron - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: Ralph Cameron ral...@igs.net; dan kwok dk...@intetron.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Monday, January 15, 2001 10:34 PM Subject: Re: Site Correlation 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 ral...@igs.net To: Ken Javor ken.ja...@emccompliance.com, Dan Kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org 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 ken.ja...@emccompliance.com To: Dan Kwok dk...@intetron.com; Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com To: Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com 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
Re: Site Correlation
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 ral...@igs.net To: Ken Javor ken.ja...@emccompliance.com, Dan Kwok dk...@intetron.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org 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 ken.ja...@emccompliance.com To: Dan Kwok dk...@intetron.com; Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com To: Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail
Re: Site Correlation
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 ken.ja...@emccompliance.com To: Dan Kwok dk...@intetron.com; Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com To: Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org
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 dk...@intetron.com To: Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
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 dk...@intetron.com To: Ralph Cameron ral...@igs.net Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dk...@intetron.com 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
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 dk...@intetron.com 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
I am quite familiar with 61000-4-6. But it is an immunity requirement and has nothing to do with the current thread, which is about controlling cm EMISSIONS on cables. I suppose one could use a CDN designed for injection as a measurement tool, but the absorbing clamp is so superior - it can be used on all types of cables, and it works up to 1 GHz, whereas CDNs are designed for no more than 230 MHz. The fact that the CDN works well below 30 MHz, all the way down to 150 kHz is immaterial - RE requirements start at 30 MHz, and in any case the absorbing clamp makes a superb current probe at 150 kHz - anyone wanting a transfer impedance for that device let me know. For those interested, my website includes a quite complete discussion on the pros and cons of using conducted techniques to simulate radiated immunity coupling, with a discussion of the corresponding emissions discussion in the introduction. Go to www.emccompliance.com, push the EMC INFO button, select the download page, and skip to the last selectable item, which is a paper I presented at the '97 IEEE EMC show in Austin, On Field-To-Wire Coupling Versus Conducted Injection Techniques. Ken Javor -- From: CE-test - Ing. Gert Gremmen - ce-marking and more... cet...@cetest.nl To: Ken Javor ken.ja...@emccompliance.com, Cortland Richmond 72146@compuserve.com, ieee pstc list emc-p...@ieee.org Subject: RE: Site Correlation Date: Sun, Jan 14, 2001, 1:10 PM Hi Ken, Again you should definitely study EN 61000-4-6. It assumes cable to have an impedance level (CM) of 150 Ohms, a good average for many situations. It uses a coupling/decoupling network matched to 150 ohms that feeds RF interference from or to the cable in common mode. Many CDN's exist therefore adapted to the cable type. The CDN approach makes high reproducibility possible, as it is not very difficult to maintain a stable 150 Ohm real impedance up till say 100 MHz. For complex cable types a current clamp is used in a special version. Using low generator voltages high level immunity test are allowed, due to the resistive coupling. The basic CDN consist of only 3 components 1 R, 1 C and 1 L. Due to the well defined CM impedances and because cables leaving the EUT are lead over a ground plane at 30 mm height, the wire part up till the CDN is not much losing it's power (characteristic impedance) over the 30 cm allowed to the CDN. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Sunday, January 14, 2001 12:45 AM To: Cortland Richmond; ieee pstc list Subject: Re: Site Correlation 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 72146@compuserve.com To: Ken Javor ken.ja...@emccompliance.com, ieee pstc list emc-p...@ieee.org 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
RE: Site Correlation
Hi Ken, Again you should definitely study EN 61000-4-6. It assumes cable to have an impedance level (CM) of 150 Ohms, a good average for many situations. It uses a coupling/decoupling network matched to 150 ohms that feeds RF interference from or to the cable in common mode. Many CDN's exist therefore adapted to the cable type. The CDN approach makes high reproducibility possible, as it is not very difficult to maintain a stable 150 Ohm real impedance up till say 100 MHz. For complex cable types a current clamp is used in a special version. Using low generator voltages high level immunity test are allowed, due to the resistive coupling. The basic CDN consist of only 3 components 1 R, 1 C and 1 L. Due to the well defined CM impedances and because cables leaving the EUT are lead over a ground plane at 30 mm height, the wire part up till the CDN is not much losing it's power (characteristic impedance) over the 30 cm allowed to the CDN. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Sunday, January 14, 2001 12:45 AM To: Cortland Richmond; ieee pstc list Subject: Re: Site Correlation 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 72146@compuserve.com To: Ken Javor ken.ja...@emccompliance.com, ieee pstc list emc-p...@ieee.org 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:ken.ja...@emccompliance.com Subj: Re: Site Correlation Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 Date: Sat, 13 Jan 2001 02:43:51 -0600 Subject: Re: Site Correlation From: Ken Javor ken.ja...@emccompliance.com Reply-To: Ken Javor ken.ja...@emccompliance.com 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
Re: Site Correlation
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 ral...@igs.net To: Ken Javor ken.ja...@emccompliance.com, David Heald dhe...@curtis-straus.com, Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org 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 ken.ja...@emccompliance.com To: David Heald dhe...@curtis-straus.com; Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dhe...@curtis-straus.com To: Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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
Re: Site Correlation
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 ken.ja...@emccompliance.com To: David Heald dhe...@curtis-straus.com; Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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 dhe...@curtis-straus.com To: Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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
Re: Site Correlation
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 72146@compuserve.com To: Ken Javor ken.ja...@emccompliance.com, ieee pstc list emc-p...@ieee.org 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:ken.ja...@emccompliance.com Subj: Re: Site Correlation Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 Date: Sat, 13 Jan 2001 02:43:51 -0600 Subject: Re: Site Correlation From: Ken Javor ken.ja...@emccompliance.com Reply-To: Ken Javor ken.ja...@emccompliance.com 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 dhe...@curtis-straus.com To: Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Subject: Re: Site Correlation Date: Fri
Re: Site Correlation
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:ken.ja...@emccompliance.com Subj: Re: Site Correlation Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 List-Post: emc-pstc@listserv.ieee.org Date: Sat, 13 Jan 2001 02:43:51 -0600 Subject: Re: Site Correlation From: Ken Javor ken.ja...@emccompliance.com Reply-To: Ken Javor ken.ja...@emccompliance.com 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 dhe...@curtis-straus.com To: Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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
Re: Site Correlation
I am familiar with the fact that the method exists, and I am familiar with the fact that the clamp is not used as a current probe - I calibrated it as one and used it that way, and it was quite satisfactory. What I was alluding to is that although the test method exists, it is not used in lieu of the RE technique or limit anywhere over the 30 - 1000 MHz range. Ken Javor -- From: CE-test - Ing. Gert Gremmen - ce-marking and more... cet...@cetest.nl To: Ken Javor ken.ja...@emccompliance.com, david heald dhe...@curtis-straus.com, tudor, allen allen_tu...@adc.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Sat, Jan 13, 2001, 12:42 PM Hello Ken, BTW did you read CISPR16 ? It describes this method in detail including calibration and construction details of what is commercially available called Luthi Clamp, after the inventor. It is prescribed as test method in CISPR 14 for household equipment up to if i remember well 230 Mhz. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Saturday, January 13, 2001 6:01 PM To: CE-test - Ing. Gert Gremmen - ce-marking and more...; david heald; tudor, allen Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I have to admit that I used an absorbing clamp as a current probe, but only up to 200 MHz. I compared it to a conventional probe at multiple locations along the cable, and I got very repeatable results fairly independent of line length related standing waves (3 meter coax terminated in N connectors to L-brackets bonded to a ground plane). This was a laboratory experiment where I used an injection clamp to drive rf current on to the shield and monitored peaks and nulls with the conventional probe and the absorbing clamp. I can supply test data to interested parties (I adhere to the prohibition against mass mailings with attachments for this service). The test data shows that the absorbing clamp smoothes out the standing wave problem and there is no reason in my mind to expect performance deterioration above 200 MHz. I was able to get the absorbing clamp arbitrarily close to the injection clamp, and as Ing. Gremmen astutely points out, this would not always be possible with real cables connected to real EUTs. Nevertheless it seems a promising technique, especially as, again as Ing. Gremmen points out, only the first fractional wavelength of cable is important to radiation, and therefore at higher frequencies the cable lay should be easier to optimize for maximum radiation (or if not optimized, then it should be able to be standardized). Ken Javor -- From: CE-test - Ing. Gert Gremmen - ce-marking and more... cet...@cetest.nl To: Ken Javor ken.ja...@emccompliance.com, David Heald dhe...@curtis-straus.com, Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Sat, Jan 13, 2001, 9:08 AM You analysis of the situation is correct but for one thing: In real life you cannot measure the current from a cable using a current clamp above approx 300 Mhz for several reasons. - physical limitations between current clamp size, coil inductance and parasitic capacitance make the behavior off all but very small (10 mm) clamps unpredictable above 300 Mhz (rule of thumb) - most of the emission of a cable can be achieved in the first 1/4 lambda of the cable at 1000 Mhz this is 7.5 cm. ( just dipole equation) To be able to get at least 90% of the current that initially flows on to the cable, one needs to approach the cable exit to 7.5 mm. This is physically impossible but for laboratory measurements. Of course on longer cables this current will have many peaks and nulls on the cable length, but some energy has already left the cable... This approach is therefore limited to lower frequencies. The immunity test standard EN 61000-4-6 follows this approach using CDN's up to 80 Mhz and 230 Mhz for some equipment. The same approach would be very practical for small EUTs and emission. This standard in coordination with EN 61000-4-3 affectively presumes that most immunity problems are caused by CM current son cables below 80 MHz and by Cabinet coupling AND CM cable current above 80 Mhz. As both emission and immunity behavior is determined by passive networks, the whole system is reciprocal. Therefore if one accepts immunity tests using this presumption, there is no reason to use the same reasoning for emission measurements. I personally want to emphasize that my personal contribution in the IEC EMC standardization groups follows this approach. As for 80 Mhz and up
RE: Site Correlation
Hello Ken, BTW did you read CISPR16 ? It describes this method in detail including calibration and construction details of what is commercially available called Luthi Clamp, after the inventor. It is prescribed as test method in CISPR 14 for household equipment up to if i remember well 230 Mhz. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Saturday, January 13, 2001 6:01 PM To: CE-test - Ing. Gert Gremmen - ce-marking and more...; david heald; tudor, allen Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I have to admit that I used an absorbing clamp as a current probe, but only up to 200 MHz. I compared it to a conventional probe at multiple locations along the cable, and I got very repeatable results fairly independent of line length related standing waves (3 meter coax terminated in N connectors to L-brackets bonded to a ground plane). This was a laboratory experiment where I used an injection clamp to drive rf current on to the shield and monitored peaks and nulls with the conventional probe and the absorbing clamp. I can supply test data to interested parties (I adhere to the prohibition against mass mailings with attachments for this service). The test data shows that the absorbing clamp smoothes out the standing wave problem and there is no reason in my mind to expect performance deterioration above 200 MHz. I was able to get the absorbing clamp arbitrarily close to the injection clamp, and as Ing. Gremmen astutely points out, this would not always be possible with real cables connected to real EUTs. Nevertheless it seems a promising technique, especially as, again as Ing. Gremmen points out, only the first fractional wavelength of cable is important to radiation, and therefore at higher frequencies the cable lay should be easier to optimize for maximum radiation (or if not optimized, then it should be able to be standardized). Ken Javor -- From: CE-test - Ing. Gert Gremmen - ce-marking and more... cet...@cetest.nl To: Ken Javor ken.ja...@emccompliance.com, David Heald dhe...@curtis-straus.com, Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Sat, Jan 13, 2001, 9:08 AM You analysis of the situation is correct but for one thing: In real life you cannot measure the current from a cable using a current clamp above approx 300 Mhz for several reasons. - physical limitations between current clamp size, coil inductance and parasitic capacitance make the behavior off all but very small (10 mm) clamps unpredictable above 300 Mhz (rule of thumb) - most of the emission of a cable can be achieved in the first 1/4 lambda of the cable at 1000 Mhz this is 7.5 cm. ( just dipole equation) To be able to get at least 90% of the current that initially flows on to the cable, one needs to approach the cable exit to 7.5 mm. This is physically impossible but for laboratory measurements. Of course on longer cables this current will have many peaks and nulls on the cable length, but some energy has already left the cable... This approach is therefore limited to lower frequencies. The immunity test standard EN 61000-4-6 follows this approach using CDN's up to 80 Mhz and 230 Mhz for some equipment. The same approach would be very practical for small EUTs and emission. This standard in coordination with EN 61000-4-3 affectively presumes that most immunity problems are caused by CM current son cables below 80 MHz and by Cabinet coupling AND CM cable current above 80 Mhz. As both emission and immunity behavior is determined by passive networks, the whole system is reciprocal. Therefore if one accepts immunity tests using this presumption, there is no reason to use the same reasoning for emission measurements. I personally want to emphasize that my personal contribution in the IEC EMC standardization groups follows this approach. As for 80 Mhz and up shielded rooms behave much more consistent and reproducible, test costs using this approach are cheaper (smaller rooms) and quicker. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Saturday, January 13, 2001 9:44 AM To: David Heald; Tudor, Allen Cc: EMC-PCST (E-mail) Subject: Re: Site Correlation I must say that this thread has been a refreshing
Re: Site Correlation
I have to admit that I used an absorbing clamp as a current probe, but only up to 200 MHz. I compared it to a conventional probe at multiple locations along the cable, and I got very repeatable results fairly independent of line length related standing waves (3 meter coax terminated in N connectors to L-brackets bonded to a ground plane). This was a laboratory experiment where I used an injection clamp to drive rf current on to the shield and monitored peaks and nulls with the conventional probe and the absorbing clamp. I can supply test data to interested parties (I adhere to the prohibition against mass mailings with attachments for this service). The test data shows that the absorbing clamp smoothes out the standing wave problem and there is no reason in my mind to expect performance deterioration above 200 MHz. I was able to get the absorbing clamp arbitrarily close to the injection clamp, and as Ing. Gremmen astutely points out, this would not always be possible with real cables connected to real EUTs. Nevertheless it seems a promising technique, especially as, again as Ing. Gremmen points out, only the first fractional wavelength of cable is important to radiation, and therefore at higher frequencies the cable lay should be easier to optimize for maximum radiation (or if not optimized, then it should be able to be standardized). Ken Javor -- From: CE-test - Ing. Gert Gremmen - ce-marking and more... cet...@cetest.nl To: Ken Javor ken.ja...@emccompliance.com, David Heald dhe...@curtis-straus.com, Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Sat, Jan 13, 2001, 9:08 AM You analysis of the situation is correct but for one thing: In real life you cannot measure the current from a cable using a current clamp above approx 300 Mhz for several reasons. - physical limitations between current clamp size, coil inductance and parasitic capacitance make the behavior off all but very small (10 mm) clamps unpredictable above 300 Mhz (rule of thumb) - most of the emission of a cable can be achieved in the first 1/4 lambda of the cable at 1000 Mhz this is 7.5 cm. ( just dipole equation) To be able to get at least 90% of the current that initially flows on to the cable, one needs to approach the cable exit to 7.5 mm. This is physically impossible but for laboratory measurements. Of course on longer cables this current will have many peaks and nulls on the cable length, but some energy has already left the cable... This approach is therefore limited to lower frequencies. The immunity test standard EN 61000-4-6 follows this approach using CDN's up to 80 Mhz and 230 Mhz for some equipment. The same approach would be very practical for small EUTs and emission. This standard in coordination with EN 61000-4-3 affectively presumes that most immunity problems are caused by CM current son cables below 80 MHz and by Cabinet coupling AND CM cable current above 80 Mhz. As both emission and immunity behavior is determined by passive networks, the whole system is reciprocal. Therefore if one accepts immunity tests using this presumption, there is no reason to use the same reasoning for emission measurements. I personally want to emphasize that my personal contribution in the IEC EMC standardization groups follows this approach. As for 80 Mhz and up shielded rooms behave much more consistent and reproducible, test costs using this approach are cheaper (smaller rooms) and quicker. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Saturday, January 13, 2001 9:44 AM To: David Heald; Tudor, Allen Cc: EMC-PCST (E-mail) 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
RE: Site Correlation
You analysis of the situation is correct but for one thing: In real life you cannot measure the current from a cable using a current clamp above approx 300 Mhz for several reasons. - physical limitations between current clamp size, coil inductance and parasitic capacitance make the behavior off all but very small (10 mm) clamps unpredictable above 300 Mhz (rule of thumb) - most of the emission of a cable can be achieved in the first 1/4 lambda of the cable at 1000 Mhz this is 7.5 cm. ( just dipole equation) To be able to get at least 90% of the current that initially flows on to the cable, one needs to approach the cable exit to 7.5 mm. This is physically impossible but for laboratory measurements. Of course on longer cables this current will have many peaks and nulls on the cable length, but some energy has already left the cable... This approach is therefore limited to lower frequencies. The immunity test standard EN 61000-4-6 follows this approach using CDN's up to 80 Mhz and 230 Mhz for some equipment. The same approach would be very practical for small EUTs and emission. This standard in coordination with EN 61000-4-3 affectively presumes that most immunity problems are caused by CM current son cables below 80 MHz and by Cabinet coupling AND CM cable current above 80 Mhz. As both emission and immunity behavior is determined by passive networks, the whole system is reciprocal. Therefore if one accepts immunity tests using this presumption, there is no reason to use the same reasoning for emission measurements. I personally want to emphasize that my personal contribution in the IEC EMC standardization groups follows this approach. As for 80 Mhz and up shielded rooms behave much more consistent and reproducible, test costs using this approach are cheaper (smaller rooms) and quicker. Regards, Gert Gremmen, (Ing) ce-test, qualified testing === Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ === -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Saturday, January 13, 2001 9:44 AM To: David Heald; Tudor, Allen Cc: EMC-PCST (E-mail) 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 dhe...@curtis-straus.com To: Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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
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 dhe...@curtis-straus.com To: Tudor, Allen allen_tu...@adc.com Cc: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message
RE: Site Correlation
Interesting... we are gojng to set-up a pre-compliance semi-anechoic chamber for 3 m measurements (mainly radiated emissions) on telecom products and we'll need to correlate it with a 10m full-compliant chamber. Our DUT's are typically sub-rack or 2m+ high telecom racks. Your idea of considering a fully anechoic vs semi-anechoic chamber sounds pretty interesting to me. We are limited in height to about 2 m (chamber internal space) so we are not able to maximize with a limited antenna height scanning. So rotating the EUT and adding 6 dB for the missing in-phase floor reflection sounds reasonable... unless I'm missing something I heard some time ago about a correlation study btw fully- and semi-anechoic rooms performed by CISPR subcommittee A and if I remember well they came up with disturbing increased uncertainties / variancies related to cables layout due to missing coupling between cables and ground floor (image theory and stuff...). Anyone who can fill me in more with this would be welcome ! Regards, Paolo Roncone At 10:37 AM 1/11/01 -0500, David Heald wrote: Hello all There are a few variables that need to be addressed to answer this question. The first is the nature of the chamber. My reply will assume that this is a fully anechoic chamber (walls, floor, and ceiling all lined with absorber material). Otherwise, all bets are off due to the unpredictable reflections from the surfaces in the chamber. In a chamber this size, I will also assume that the antenna height is fixed, or at least not very adjustable. Given a fully anechoic room and a fixed antenna height, theoretically you should be able to extrapolate (about 10 dB from 1 to 3 meters antenna distance and another 10 dB from 3 to 10 meters) with only about 6 dB of uncertainty. In practice this is usually accurate but real world conditions have slightly more uncertainty so 10 dB is a fairly safe margin to use. A few things to keep in mind: if the chamber is only semi-anechoic (walls and ceiling lined) you will have more uncertainty due to possible cancellation due to floor reflections. At this point, relative change or frequency identification is about the only thing the chamber is good for. Also, near field readings can be significantly different from far-field readings. If you come up with marginal near field readings, be prepared for the worst when you take 10m readings. Finally, be sure to check BOTH antenna polarities. I hope this helps Usual employer disclaimer . . . 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 http://www.curtis-straus.comwww.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: mailto:allen_tu...@adc.comallen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org! with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: mailto:jim_bac...@mail.monarch.comjim_bac...@mail.monarch.com Michael Garretson:mailto:pstc_ad...@garretson.orgpstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: mailto:ri...@ieee.orgri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
Joe, If the transmitting antenna (your product) and the receiving antenna were in free space, you pretty much could assume that the radiation falls off at 1/r^2, and thus use a 10.5dB correction factor between 10m and 3m measurements. (You might have to worry about near-field effects and antenna interaction at low frequencies.) But Radiated Emissions measurements for equipment are done over a ground plane. Thus the receiving antenna sees: * Direct radiation from the equipment. AND * Radiation that has bounced off the ground plane. Because of the difference in path lengths, these signals may sum anywhere from exactly in-phase to exactly out-of-phase, depending on the frequency and antenna heights. For horizontal antennas this turns out to be just a small disturbing factor, less than 1dB or so. But vertical antennas can see anywhere from 200% to 0% of the free-space voltage for that same position of the antennas. Because the FCC and CISPR regulations require you to vary the receive antenna height between 1m and 4m, you will see lobes in the vertical pattern because of this constructive/destructive interference. After having some of our products pass easily in our 3m chamber, and then fail miserably on a 10m test site, our EMC folks came up with an additional correction for: * Transmitting antenna height of 1m (tabletop product on 0.8m high table). * Receive antenna height of 1-1.75m in our 3m chamber. * Receive antenna height of 1-4m on a 10m site. * Frequencies from 30MHz to 1GHz. This Vertical Correction Factor (VCF) is: * About 1dB at 30MHz. * About 7dB at 200MHz. * About 1dB at 1GHZ. Thus, if I am testing a product in our 3m chamber, and want to be sure that it will pass the official tests at 10m, at 200MHz I had better see vertical emissions no higher than 3.5dB (10.5dB for 1/r^2 minus 7dB VCF) above the 10m limit. Because of Murphy's Law, and to protect us from slight variations in production, our EMC folks like us to have 4dB margin against this corrected limit. If we are within 2dB of this corrected limit, we may pass Radiated Emissions tests on the initial units, but will have to rerun A-B Radiated Emissions tests in our 3m chamber for *any* contemplated changes to the product, and may have to test production units regularly to make sure that we stay legal. This is not a fun way for us Design Engineers to spend our time... Thus we tend to overdesign the products, which adds cost. We have had a 10m Open Air Test Site (OATS) here for a number of years. But because of Kentucky weather, we could only count on being able to use it about 5-6 months per year. For another couple of months per year we could hope/pray for a warm day to run 10m tests, but expected to have to travel to a closed-in 10m test site. But, in late October we started construction of a new lab building that will have a completely-equipped 10m semi-anechoic/anechoic chamber. It's supposed to be completed in late summer. Yeehah! John Barnes Advisory Engineer Lexmark International --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
I'd say either a comb generator, or a sweep generator but use them to excite a test object of the same general size as the equipment you wish to test. The smaller your chamber, the more it will be affected by the size of an EUT sitting in it. If you can be pretty sure what you will test, add its cables, too. And no, I'd give the same answer for both. That's my two-cents worth, anyway. Cortland == Original Message Follows (Headers snipped) 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
We are also in the process of setting up a 3 meter indoor site. Would it not be better to compare a 3 meter site to a 3 meter site vs a 10 meter site and add 10db to your limit line? Joe Martin Neven Pischl npis...@cisco.com@ieee.org on 01/11/2001 08:12:38 AM Please respond to Neven Pischl npis...@cisco.com Sent by: owner-emc-p...@ieee.org To: Tudor, Allen allen_tu...@adc.com, EMC-PCST (E-mail) emc-p...@majordomo.ieee.org cc: Subject: Re: Site Correlation Allen, the main problem you will have is not whether to use signal generator or a comb generator, but the difference in the radiation characteristic of your source for correlation and the DUTs that you will later put in the chamber. You will measure a lots of near-field in you 3m or smaller chamber. The field pattern at 10 m will be very different. Correlation from near-field to far-field obtained with source of one (near-field) radiation characteristics can not be used to predict 10 m radiation of a source with very different (near-field) radiation characteristics. To answer your question directly first, the best would be if you could use a network analyzer or a spectrum analyzer with a tracking generator, so that you can do swept measurement. However, the way you generate your test field will make huge difference to the test results. If you use a certain transmit antenna for your test (correlation), you will get the correlation for that antenna, but not for a DUT that you might want to test (and use the correlation) later. I suggest you take your typical product, physically configure it as in your typical test setup, it may but does not have be powered. Then couple your signal source (whatever you choose to use) to the DUT PCB and wiring (here you have to be a little creative) and do the measurement. Then you can repeat the same at 10 m site. By doing that you will be ale to get correlation for that particular kind of DUT. However, if you obtain your correlation with a DSL modem (e.g. a small box with one power, one DSL, and one UTP cable) on a wooden 80 cm high turntable, you can not use it to predict 10 m radiation of a rack-mount multi-port Ethernet switch or any other DUT that is physically much different. If you do it like that, and run your test a few times, you will soon gain experience (some will be from the obtain correlation and some will be your developed feeling) that you can use to correlate your product measured in your precompliance chamber to 10 m. I suggest you plot your predicted data (obtained from the correlation measurement) versus measured over each other every time you do it (at least for the first 5-10 tests), and it will show you the spread (uncertainty) of your correlation. Hope this will help you, Neven - Original Message - From: Tudor, Allen allen_tu...@adc.com To: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Thursday, January 11, 2001 5:58 AM Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
My understanding is that quite good correlation can be drawn between three and ten meter sites, as long as the EUT is in the far field of the antenna AND the antenna is in the far field of the EUT at both separation distances. However, if this is not the case, then you have problems. -- From: Brent Pahl bre...@dynarc.com To: Ken Javor ken.ja...@emccompliance.com, Tudor, Allen allen_tu...@adc.com, EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Thu, Jan 11, 2001, 1:31 PM Hi Ken, Very true. I was simply looking at the question of which of the two listed methods would work best, without taking into account the overall accuracy of either method. No matter what you try, you will never get direct correlation between a 10m OATS and a 3m chamber, but by utilizing one of the listed methods, he may get a slightly clearer picture than he would without any correction factors at all. The measurements from the 3m chamber will always need to be taken with a grain of salt. Regards, Brent -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Thursday, January 11, 2001 11:02 AM To: Brent Pahl; Tudor, Allen; EMC-PCST (E-mail) Subject: Re: Site Correlation Have to take strong exception. If EUT is much larger than comb generator, a correlation between sites using the comb generator will not work for the larger EUT. Measurement antenna is in far field of comb generator on both sites, but is more in the far field of the EUT at 10 m than at 3 m. -- From: Brent Pahl bre...@dynarc.com To: Tudor, Allen allen_tu...@adc.com, EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Thu, Jan 11, 2001, 11:31 AM Allen, We just did this in our 3-meter lab using a comb generator. After interviewing several test labs, I found out that they use comb generator's occasionally to see if they are still properly calibrated. Evidently, a good comb generator will give a consistent output, give or take 0.5dB, over it's lifetime. As long as the comb generator is consistently set up the same way every time (e.g. with power cord vs. on battery, same distance from antenna, facing same direction), and the measurements are taken the same way at the 10m site as they are in your 3m chamber (e.g. not maximizing at every frequency vs. maximizing at every frequency, peak hold vs. continuous run), you should get consistent results. In regards to the vs. options listed above, I would recommend using the 1st option in all cases. Honestly, either a comb generator or a signal-generator/antenna should both give you accurate results, but the comb generator reduces the number of variables you need to consider/double-check during setup. Best of luck, Brent -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Tudor, Allen Sent: Thursday, January 11, 2001 5:58 AM To: EMC-PCST (E-mail) Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy
RE: Site Correlation
Hi Ken, Very true. I was simply looking at the question of which of the two listed methods would work best, without taking into account the overall accuracy of either method. No matter what you try, you will never get direct correlation between a 10m OATS and a 3m chamber, but by utilizing one of the listed methods, he may get a slightly clearer picture than he would without any correction factors at all. The measurements from the 3m chamber will always need to be taken with a grain of salt. Regards, Brent -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Thursday, January 11, 2001 11:02 AM To: Brent Pahl; Tudor, Allen; EMC-PCST (E-mail) Subject: Re: Site Correlation Have to take strong exception. If EUT is much larger than comb generator, a correlation between sites using the comb generator will not work for the larger EUT. Measurement antenna is in far field of comb generator on both sites, but is more in the far field of the EUT at 10 m than at 3 m. -- From: Brent Pahl bre...@dynarc.com To: Tudor, Allen allen_tu...@adc.com, EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Thu, Jan 11, 2001, 11:31 AM Allen, We just did this in our 3-meter lab using a comb generator. After interviewing several test labs, I found out that they use comb generator's occasionally to see if they are still properly calibrated. Evidently, a good comb generator will give a consistent output, give or take 0.5dB, over it's lifetime. As long as the comb generator is consistently set up the same way every time (e.g. with power cord vs. on battery, same distance from antenna, facing same direction), and the measurements are taken the same way at the 10m site as they are in your 3m chamber (e.g. not maximizing at every frequency vs. maximizing at every frequency, peak hold vs. continuous run), you should get consistent results. In regards to the vs. options listed above, I would recommend using the 1st option in all cases. Honestly, either a comb generator or a signal-generator/antenna should both give you accurate results, but the comb generator reduces the number of variables you need to consider/double-check during setup. Best of luck, Brent -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Tudor, Allen Sent: Thursday, January 11, 2001 5:58 AM To: EMC-PCST (E-mail) Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
Have to take strong exception. If EUT is much larger than comb generator, a correlation between sites using the comb generator will not work for the larger EUT. Measurement antenna is in far field of comb generator on both sites, but is more in the far field of the EUT at 10 m than at 3 m. -- From: Brent Pahl bre...@dynarc.com To: Tudor, Allen allen_tu...@adc.com, EMC-PCST \(E-mail\) emc-p...@majordomo.ieee.org Subject: RE: Site Correlation Date: Thu, Jan 11, 2001, 11:31 AM Allen, We just did this in our 3-meter lab using a comb generator. After interviewing several test labs, I found out that they use comb generator's occasionally to see if they are still properly calibrated. Evidently, a good comb generator will give a consistent output, give or take 0.5dB, over it's lifetime. As long as the comb generator is consistently set up the same way every time (e.g. with power cord vs. on battery, same distance from antenna, facing same direction), and the measurements are taken the same way at the 10m site as they are in your 3m chamber (e.g. not maximizing at every frequency vs. maximizing at every frequency, peak hold vs. continuous run), you should get consistent results. In regards to the vs. options listed above, I would recommend using the 1st option in all cases. Honestly, either a comb generator or a signal-generator/antenna should both give you accurate results, but the comb generator reduces the number of variables you need to consider/double-check during setup. Best of luck, Brent -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Tudor, Allen Sent: Thursday, January 11, 2001 5:58 AM To: EMC-PCST (E-mail) Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
RE: Site Correlation
Allen, We just did this in our 3-meter lab using a comb generator. After interviewing several test labs, I found out that they use comb generator's occasionally to see if they are still properly calibrated. Evidently, a good comb generator will give a consistent output, give or take 0.5dB, over it's lifetime. As long as the comb generator is consistently set up the same way every time (e.g. with power cord vs. on battery, same distance from antenna, facing same direction), and the measurements are taken the same way at the 10m site as they are in your 3m chamber (e.g. not maximizing at every frequency vs. maximizing at every frequency, peak hold vs. continuous run), you should get consistent results. In regards to the vs. options listed above, I would recommend using the 1st option in all cases. Honestly, either a comb generator or a signal-generator/antenna should both give you accurate results, but the comb generator reduces the number of variables you need to consider/double-check during setup. Best of luck, Brent -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Tudor, Allen Sent: Thursday, January 11, 2001 5:58 AM To: EMC-PCST (E-mail) Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
RE: Site Correlation
I would assume that the 10m semi-anechoic chamber complies with ANSI C63.4 volumetric NSA. I would also assume that the 3m chamber noes not comply. The major correlation issues would relate to: 1) 3m versus 10m (regardless of the sites) 2) non-compliant room (with peaks and nulls) versus compliant site (meets NSA) 3) antenna geometry (Bilog, bicon, log-periodic) There are lots more reasons but I believe these to be the major reasons for difficulty in correlation. A comb generator with fixed antenna is more reproducible than signal generator and antenna as part of the correlation issue is also the personell performing the test. Think about the York CNE (Constant Noise Emitter) which puts out junk continuously up to 2 GHz. With it, you can see any resonances between the sites (if they exist) and you can develop as good a correlation factor as is probably possible. Good Luck. -Original Message- From: Tudor, Allen [mailto:allen_tu...@adc.com] Sent: Thursday, January 11, 2001 8:58 AM To: EMC-PCST (E-mail) Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
If you don't use a source of similar size to the EUT you won't get the right answer. -- From: Tudor, Allen allen_tu...@adc.com To: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Subject: Site Correlation Date: Thu, Jan 11, 2001, 7:58 AM 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
Allen, the main problem you will have is not whether to use signal generator or a comb generator, but the difference in the radiation characteristic of your source for correlation and the DUTs that you will later put in the chamber. You will measure a lots of near-field in you 3m or smaller chamber. The field pattern at 10 m will be very different. Correlation from near-field to far-field obtained with source of one (near-field) radiation characteristics can not be used to predict 10 m radiation of a source with very different (near-field) radiation characteristics. To answer your question directly first, the best would be if you could use a network analyzer or a spectrum analyzer with a tracking generator, so that you can do swept measurement. However, the way you generate your test field will make huge difference to the test results. If you use a certain transmit antenna for your test (correlation), you will get the correlation for that antenna, but not for a DUT that you might want to test (and use the correlation) later. I suggest you take your typical product, physically configure it as in your typical test setup, it may but does not have be powered. Then couple your signal source (whatever you choose to use) to the DUT PCB and wiring (here you have to be a little creative) and do the measurement. Then you can repeat the same at 10 m site. By doing that you will be ale to get correlation for that particular kind of DUT. However, if you obtain your correlation with a DSL modem (e.g. a small box with one power, one DSL, and one UTP cable) on a wooden 80 cm high turntable, you can not use it to predict 10 m radiation of a rack-mount multi-port Ethernet switch or any other DUT that is physically much different. If you do it like that, and run your test a few times, you will soon gain experience (some will be from the obtain correlation and some will be your developed feeling) that you can use to correlate your product measured in your precompliance chamber to 10 m. I suggest you plot your predicted data (obtained from the correlation measurement) versus measured over each other every time you do it (at least for the first 5-10 tests), and it will show you the spread (uncertainty) of your correlation. Hope this will help you, Neven - Original Message - From: Tudor, Allen allen_tu...@adc.com To: EMC-PCST (E-mail) emc-p...@majordomo.ieee.org Sent: Thursday, January 11, 2001 5:58 AM Subject: Site Correlation 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: allen_tu...@adc.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Site Correlation
Hello all There are a few variables that need to be addressed to answer this question. The first is the nature of the chamber. My reply will assume that this is a fully anechoic chamber (walls, floor, and ceiling all lined with absorber material). Otherwise, all bets are off due to the unpredictable reflections from the surfaces in the chamber. In a chamber this size, I will also assume that the antenna height is fixed, or at least not very adjustable. Given a fully anechoic room and a fixed antenna height, theoretically you should be able to extrapolate (about 10 dB from 1 to 3 meters antenna distance and another 10 dB from 3 to 10 meters) with only about 6 dB of uncertainty. In practice this is usually accurate but real world conditions have slightly more uncertainty so 10 dB is a fairly safe margin to use. A few things to keep in mind: if the chamber is only semi-anechoic (walls and ceiling lined) you will have more uncertainty due to possible cancellation due to floor reflections. At this point, relative change or frequency identification is about the only thing the chamber is good for. Also, near field readings can be significantly different from far-field readings. If you come up with marginal near field readings, be prepared for the worst when you take 10m readings. Finally, be sure to check BOTH antenna polarities. I hope this helps Usual employer disclaimer . . .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 3mchamber) to a 10m anechoic chamber? Should I use a signal generator andantenna or should I use a comb generator?Would the answer be different if I were correlating the pre-compliancechamber to an OATS?Thanks in advance.Allen Tudor, Compliance EngineerADC DSL Systems Inc.6531 Meridien Dr. Raleigh, NC 27616phone: 919.875.3382email: allen_tu...@adc.com---This message is from the IEEE EMC Society Product SafetyTechnical Committee emc-pstc discussion list.To cancel your subscription, send mail to: majord...@ieee.org! with the single line: unsubscribe emc-pstcFor help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.orgFor policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
