Yes, two chokes were the next step. That worked fine, but we had the room to build suppression into each box behind the connectors, so we didn't really end up with a cable with a lump at both ends.
Ed > -----Original Message----- > From: Ralph Cameron [SMTP:ral...@igs.net] > Sent: Thursday, December 02, 1999 5:39 PM > To: Price, Ed; d...@dsmith.org > Cc: emc-pstc > Subject: Re: Ferrites can increase emissions? > > In such a case did you place a ferrite device at both ends of the cable? > It > has worked for me. > Ralph > > ----- Original Message ----- > From: Price, Ed <ed.pr...@cubic.com> > To: 'Ralph Cameron' <ral...@igs.net>; <d...@dsmith.org> > Cc: emc-pstc <emc-p...@majordomo.ieee.org> > Sent: Thursday, December 02, 1999 12:29 PM > Subject: RE: Ferrites can increase emissions? > > > > I have had the experience of putting ferrite chokes on a cable bundle > which > > connected two parts of a system. Putting the choke close to Box A, some > > radiated emissions went down and some went up. It doesn't seem > reasonable > at > > first, until you remember that each box may be contributing some of the > > combined noise currents in the cable. The location of the choke affects > the > > size of the loops oppositely. > > > > Ed > > > > > -----Original Message----- > > > From: Ralph Cameron [SMTP:ral...@igs.net] > > > Sent: Thursday, December 02, 1999 12:10 PM > > > To: d...@dsmith.org > > > Cc: emc-pstc > > > Subject: Re: Ferrites can increase emissions? > > > > > > > > > Hi Doug: > > > > > > The term "ground loop" is misleading I agree. I meant to say coupling > and > > > by > > > placing the ferrite remotely from the source of the emissions only > serves > > > to > > > end load the conductors which will change the resonant length. > > > > > > In the case of placing the toroidal device on the power cord, right at > the > > > point of entry to the PCB, chassis, cabinet etc. the "coupling loop" > as > > > opposed to ground loop is generally broken and the harmful > ffects( device > > > malfunction) disappear. > > > > > > I guess the point I'm trying to make is why defeat the purpose of a > > > suppression device by placing it on conductors remotely from the > source > of > > > the emissions? > > > > > > Ralph > > > > > > ----- Original Message ----- > > > From: Douglas C. Smith <d...@dsmith.org> > > > To: Ralph Cameron <ral...@igs.net> > > > Cc: emc-pstc <emc-p...@majordomo.ieee.org> > > > Sent: Thursday, December 02, 1999 8:43 AM > > > Subject: Re: Ferrites can increase emissions? > > > > > > > > > > Hi Ralph and all, > > > > > > > > Please define "ground loop" in your reply below. Normally, the term > > > > ground loop only has meaning at low frequencies (60 Hz and DC). At > > > > high frequencies an infinite number of loops exist and they do not > > > > require a conductor to complete them. You need to define exactly the > > > > effect for the particular case below. > > > > > > > > The special case in my article goes a level deeper than your > > > > discussion to show that ferrites at one end of a cable can either > > > > increase or decrease emissions from equipment at the opposite end by > > > > either causing an impedance match or mismatch. No "ground loops" > > > > needed to explain this phenomenon. > > > > > > > > Doug > > > > > > > > > > > > Ralph Cameron wrote: > > > > > > > > > > The purpose of a common mode choke whether it be of ferrite or > > > powdered > > > iron > > > > > is to isolate the connecting conductors from the rest of the > mainboard > > > or > > > > > chassis. If the toridal core is correctly placed as close to the > > > source of > > > > > the emissions i.e. the PCB, the conductors which carry the emitted > > > noise > > > are > > > > > effectively isolated from high frequency noise currents to flow in > > > common > > > > > mode. The attenutaion will vary acording to the efficiency of the > > > material > > > > > selected and a permeability of a nominal 850 is useful over the > range > > > 3-40 > > > > > Mhz. > > > > > > > > > > Some of the telphone companies use common mode chokes to attempt > to > > > suppress > > > > > induced RF energy on phone lines and sometimes it works. They > alsmot > > > always > > > > > specify placement of the in line encapsulated choke (AT&T Z1000) > at > > > the > > > wall > > > > > socket. The amount of connecting cable from the phone to the wall > > > socket is > > > > > a good antenna too so picks up RF and bypasses any effect of the > > > common > > > mode > > > > > choke. Although the problem is removing the condcuted current > before > > > it > > > > > becomes a problem , the same principle applies to emitted noise. > > > > > > > > > > In some cases of suppressing consumer equipment there is a > dramatic > > > increase > > > > > in sensitvity to conducted currents at different > requencies( usually > > > > > higher) and this requires that the ground loop provided by the > power > > > cord be > > > > > isolated from the device. Inevitably this has cured the problem. > Be > > > aware > > > > > that any cabling connected to a device can radiate as well as > conduct > > > > > undesireable energy into the device. Ferrites provide a simple, > non > > > > > intrusive, inexpensive solution to such problems. You will see > them > > > on > > > all > > > > > the better quality computer monitors and laptops. > > > > > > > > > > Ralph Cameron > > > > > > > > > > Independant EMC Consultant and suppresion of consumer electronics > > > > > (After sale) > > > > > > > > > > ----- Original Message ----- > > > > > From: Douglas C. Smith <d...@dsmith.org> > > > > > To: emc-pstc <emc-p...@majordomo.ieee.org> > > > > > Sent: Wednesday, December 01, 1999 9:46 PM > > > > > Subject: Ferrites can increase emissions? > > > > > > > > > > > > > > > > > Hi All, > > > > > > > > > > > > I have noticed (like I expect many of you) that sometimes adding > a > > > > > > ferrite on a cable to suppress common mode current caused > emissions > > > > > > actually increases emissions at some frequencies. After thinking > > > about > > > > > > this and trying an experiment to confirm one mechanism, I wrote > up > > > an > > > > > > article describing that mechanism. I have posted the article on > my > > > > > > website (emcesd.com or www.dsmith.org) as the "Technical Tidbit" > > > > > > article for December. > > > > > > > > > > > > For the case shown there, a ferrite added at the OPPOSITE end of > the > > > > > > cable from EUT2 would actually reduce emissions from EUT2 at > > > frequency > > > > > > F2. Whereas if added at EUT2, emissions from EUT2 go down but go > up > > > > > > from EUT1. Sort of an unusual case. Granted this is a special > case, > > > > > > but the result is interesting and suggests lots of other > possible > > > > > > configurations with strange results. > > > > > > > > > > > > Doug > > > > > > > > > > > > -- > > > > > > ----------------------------------------------------------- > > > > > > ___ _ Doug Smith > > > > > > \ / ) P.O. Box 1457 > > > > > > ========= Los Gatos, CA 95031-1457 > > > > > > _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 > > > > > > / /\ \ ] / /\ \ Mobile: 408-858-4528 > > > > > > | q-----( ) | o | Email: d...@dsmith.org > > > > > > \ _ / ] \ _ / Website: http://www.dsmith.org > > > > > > ----------------------------------------------------------- > > > > > > > > > > > > --------- > > > > > > This message is coming from the emc-pstc discussion list. > > > > > > To cancel your subscription, send mail to majord...@ieee.org > > > > > > with the single line: "unsubscribe emc-pstc" (without the > > > > > > quotes). For help, send mail to ed.pr...@cubic.com, > > > > > > jim_bac...@monarch.com, ri...@sdd.hp.com, or > > > > > > roger.volgst...@compaq.com (the list administrators). > > > > > > > > > > > > > > > > > > > > > > > > > > > > --------- > > > > > This message is coming from the emc-pstc discussion list. > > > > > To cancel your subscription, send mail to majord...@ieee.org > > > > > with the single line: "unsubscribe emc-pstc" (without the > > > > > quotes). For help, send mail to ed.pr...@cubic.com, > > > > > jim_bac...@monarch.com, ri...@sdd.hp.com, or > > > > > roger.volgst...@compaq.com (the list administrators). > > > > > > > > -- > > > > ----------------------------------------------------------- > > > > ___ _ Doug Smith > > > > \ / ) P.O. Box 1457 > > > > ========= Los Gatos, CA 95031-1457 > > > > _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 > > > > / /\ \ ] / /\ \ Mobile: 408-858-4528 > > > > | q-----( ) | o | Email: d...@dsmith.org > > > > \ _ / ] \ _ / Website: http://www.dsmith.org > > > > ----------------------------------------------------------- :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 (Voice) 619-505-1502 (Fax) Military & Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
