Re: Source of noise
In a message dated 7/2/2003 11:23:03 PM Central Daylight Time, j...@jmwa.demon.co.uk writes: Where did you get the idea that 'CE stops at 30 MHz'? The test for *conducted emissions on the mains lead* goes up to 30 MHz. Emissions at higher frequencies are controlled by the requirements for radiated emissions. The lead is long enough to radiate reasonably efficiently above 30 MHz Simple... CE = Conducted Emissions. An Acronym long used before being associated with Europe... Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
Re: Source of noise
I read in !emc-pstc that lfresea...@aol.com wrote (in 136.21721a07.2c34 9...@aol.com) about 'Source of noise' on Wed, 2 Jul 2003: In messing around, at about 40 MHz, the PC noise is showing up on the power cord. I guess noone worries because CE stops at 30 MHz. Where did you get the idea that 'CE stops at 30 MHz'? The test for *conducted emissions on the mains lead* goes up to 30 MHz. Emissions at higher frequencies are controlled by the requirements for radiated emissions. The lead is long enough to radiate reasonably efficiently above 30 MHz. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Source of noise
Morning folks.. I find myself wrestling with PC emissions again. No names this time :-) Above 500 MHz, I'm seeing a bunch of reasonably stable harmonics with about a 33 MHz spacing. Any thoughts as to what they may be from? I've played with all the case openings etc, and also added a ferrite bead to every cable leaving the MB... only minimal effect on this particular set of emissions. Ironically, the cooling fan is a big problem, it's powered from a 5 volt source that's very noisy. Consequently, the wires going to it radiate like crazy... I believe the MotherBoard is clocking around 1 GHz. Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
RE: Source of noise
Hi Derek, 33 MHz is a standard clock frequency for PCI bus. Possible sources are; motherboard bridge to PCI connectors; motherboard bridge to PCI IC devices on the motherboard such as on board LAN, USB or audio; sometimes a PCI card will have an onboard bridge that redistributes the PCI bus to several devices on the PCI card. Typically, PCI clocks go to a single device so clock distribution IC is required. These some possible sources if it is PCI bus. Isolating the component blocks or clock lines can be a little tricky because it may shut down the complete system. Having the ability to control the firmware is very helpful. Hope this helps and good luck. RICK LINFORD rlinf...@sonicwall.com From: lfresea...@aol.com [mailto:lfresea...@aol.com] Sent: Wednesday, July 02, 2003 10:39 AM To: emc-p...@ieee.org Subject: Source of noise Morning folks.. I find myself wrestling with PC emissions again. No names this time :-) Above 500 MHz, I'm seeing a bunch of reasonably stable harmonics with about a 33 MHz spacing. Any thoughts as to what they may be from? I've played with all the case openings etc, and also added a ferrite bead to every cable leaving the MB... only minimal effect on this particular set of emissions. Ironically, the cooling fan is a big problem, it's powered from a 5 volt source that's very noisy. Consequently, the wires going to it radiate like crazy... I believe the MotherBoard is clocking around 1 GHz. Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
Re: Source of noise
In a message dated 7/2/2003 3:03:29 PM Central Daylight Time, bstu...@dlsemc.com writes: Derek, All power supplies are supposed to be tested with a representative system. They are primarily designed to filter the supply emissions, since line filters typically do little filtering above 20 or 25 MHz. Also remember the old saying, CE plus CE does NOT equal CE! Bill William M Stumpf DLS Electronics 166 South Carter St. Genoa City WI 53128 ph: 262-279-0210 fx: 262-279-3630 email: bstu...@dlsemc.com From what I've seen, I have to conclude this isn't happening... In messing around, at about 40 MHz, the PC noise is showing up on the power cord. I guess noone worries because CE stops at 30 MHz. Good to hear from you :-) Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
RE: Source of noise
Derek, All power supplies are supposed to be tested with a representative system. They are primarily designed to filter the supply emissions, since line filters typically do little filtering above 20 or 25 MHz. Also remember the old saying, CE plus CE does NOT equal CE! Bill William M Stumpf DLS Electronics 166 South Carter St. Genoa City WI 53128 ph: 262-279-0210 fx: 262-279-3630 email: bstu...@dlsemc.com From: lfresea...@aol.com [mailto:lfresea...@aol.com] Sent: Wednesday, July 02, 2003 2:16 PM To: emc-p...@ieee.org Subject: Re: Source of noise Hi All, Thanks for the great replies! looks like the PCI bus is the problem.. But here's the quandry.. Now we are adding the cards back in, they should add little to the profile, correct? After all, they all have the CE mark on them, and some have the FCC sticker too. This is not happening, in fact some emissions are quire strong.. I've also noticed that the Power supply is letting the PC noise out. I opened the power supply ( bang goes the warrenty ), and there is the minimal of filters.. Are the power supplies tested individually to carry the agency sticker?, with a real PC? or just load resistors? Are they designed to suppress the PC noise? Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
Re: Source of noise
Derek, Most of the PS manufacturers I've dealt with use passive dummy loads or quiet active loads. These very handy quiet active loads provide programmable loading, BUT IN NO WAY SIMULATE THE SUPPLY'S ACTUAL USE. In other words, how many quiet loads do you power? Almost every load is a micro or some digital electronics. I've been training my clients to inject heavy noise at their load outputs [common mode and differential mode] to make certain that their supplies are not transparent to those variable loads. Most now test some time during development with active digital loads to make certain their supplies don't pass the noise right back through the supply. Above 30MHz does not require a lot of bulk for filtering. Most of the bulk is there for the near 150KHz noise. You'll find that part selection and layout are more critical for filtering above 20MHz. I always encourage end-users to include operating specs in their PS purchase agreements to put the burden for proper design back onto the PS manufacturers. - Robert - Robert A. Macy, PEm...@california.com 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 101 E San Fernando, Suite 402 San Jose, CA 95112 On Wed, 2 Jul 2003 15:16:22 EDT lfresea...@aol.com wrote: Hi All, Thanks for the great replies! looks like the PCI bus is the problem.. But here's the quandry.. Now we are adding the cards back in, they should add little to the profile, correct? After all, they all have the CE mark on them, and some have the FCC sticker too. This is not happening, in fact some emissions are quire strong.. I've also noticed that the Power supply is letting the PC noise out. I opened the power supply ( bang goes the warrenty ), and there is the minimal of filters.. Are the power supplies tested individually to carry the agency sticker?, with a real PC? or just load resistors? Are they designed to suppress the PC noise? Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Source of noise
Hi All, Thanks for the great replies! looks like the PCI bus is the problem.. But here's the quandry.. Now we are adding the cards back in, they should add little to the profile, correct? After all, they all have the CE mark on them, and some have the FCC sticker too. This is not happening, in fact some emissions are quire strong.. I've also noticed that the Power supply is letting the PC noise out. I opened the power supply ( bang goes the warrenty ), and there is the minimal of filters.. Are the power supplies tested individually to carry the agency sticker?, with a real PC? or just load resistors? Are they designed to suppress the PC noise? Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
RE: Source of noise
Derek, Harmonics with a 33 MHz spacing would suggest a 33 MHz clock signal, even though these are very high order harmonics. The PCI (not fast PCI) bus has a 33 MHz clock. Jim James L. Knighten, Ph.D. Teradata, a divsion of NCR http://www.ncr.com 17095 Via del Campo San Diego, CA 92127 tel: 858-485-2537 fax: 858-485-3788 From: lfresea...@aol.com [mailto:lfresea...@aol.com] Sent: Wednesday, July 02, 2003 9:39 AM To: emc-p...@ieee.org Subject: Source of noise Morning folks.. I find myself wrestling with PC emissions again. No names this time :-) Above 500 MHz, I'm seeing a bunch of reasonably stable harmonics with about a 33 MHz spacing. Any thoughts as to what they may be from? I've played with all the case openings etc, and also added a ferrite bead to every cable leaving the MB... only minimal effect on this particular set of emissions. Ironically, the cooling fan is a big problem, it's powered from a 5 volt source that's very noisy. Consequently, the wires going to it radiate like crazy... I believe the MotherBoard is clocking around 1 GHz. Cheers, Derek N. Walton Owner L F Research EMC Design and Test Facility Poplar Grove, Illinois, USA www.lfresearch.com
