Charles, Yes, I do try very hard to maximize cables. However, it is not an exact science! It is also very difficult with the higher frequencies, since the radiation pattern can change drastically. If you are moving the cables and looking at the signal in real time, you will only see the signal level change for the one turntable position. It is like squeezing a ballon.
Another thing that can change the emission level is the operating mode of the device. I've seen huge differences in emissions level when different software is running, or even when different monitor modes are selected. As far as maximization falling out of favor, all I will say is that for some labs there seems to be a push to get products in and out of the door. The lab where I work now, I was pleasently surprised to see that they work very hard trying to fail a product under test. Bob Richards. --- "Grasso, Charles" <[email protected]> wrote: > > Hi Bob, > > Don't you ALWAYS maximize cables. I found that > with cable maximization my test repeatabilty > improved dramatically. > > HAs cable maximization fallen out of favour? > > > -----Original Message----- > From: [email protected] > To: [email protected] > Sent: 3/22/2005 6:58 AM > Subject: Re: Radiated Emission Testing > > It is not an unusual occurance. This is one good > reason why you want a good margin under the limit. > Most people like to see a margin of at least 6dB. > > One variable is the site itself. A good OATS is the > best. Sites can have up to 4dB variation from > theoretical, and one chamber I've been involved with > had a problem in the 50-60MHz range, where it was > 3.9dB out -- barely acceptable. You might want to > ask > to see the site attenuation data from the labs > involved. > > There can also be a big difference depending on the > measuring distance. Some standards allow > extrapolation > to be done when measuring at some distance other > than > the distance spelled out in the standard, but > looking > at the difference in theoretical site attenuation > between a 3m and a 10m site will show that linear > extrapolation is not accurate through much of the > frequency range. > > It is not unusual to get different results at the > SAME > lab, depending on the person conducting the test. > Like > it or not, some technicians are better or more > diligent when it comes to maximizing the emission by > playing with cable placement. When I worked at a > compliance test lab, I ticked off a few clients when > their product was passing by 2dB until I moved the > cables and rescanned only to fail them by 1dB. > > Bob Richards > Square D. > > --- Geetha Balasubramanian > <[email protected]> > wrote: > > Dear Experts, > > > > One of our products had been tested by an > > accredited lab at US on May 2004 and found to be > > compliant with FCC, CE & VCCI. We started mass > > manufacturing the product and it is being sold in > > the US, Europe & Japan markets for the past 6 > > months. Then came a requirement for that product > in > > Taiwan market. Since the May 2004 testing at the > US > > lab was not run in a BSMI approved system it > became > > necessary for us to retest the same product. This > > time the product has been tested in an accredited > > lab in Taiwan. The Taiwan lab tests are showing > that > > the product is not compliant to the CISPR22 and > need > > a ferrite core in the USB cable to make it > compliant > > to the standards. Product tested by the US lab & > > tested by he Taiwan lab are absolutely identical. > > As an engineer responsibled for compliancy I > > am a bit confused now. How to resolve this issue? > I > > request you experts to guide me. > > > > Sincerely > > > > Geetha Balasubramanian > > > > > This message is from the IEEE Product Safety > Engineering Society > emc-pstc discussion list. Website: > http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to > [email protected] > > Instructions: > http://listserv.ieee.org/listserv/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on > the web at: > > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
