Naftali, Are the PC's causing the issue or is it RF noise coming in on the AC line? Try unplugging the Laptops from the AC and running them on batteries to see if the noise goes away. You may need to filter the AC lines going to the support equipment. If you are testing on a make shift site you will need to filter the AC going to the EUT as well. If you can, place the support equipment off the end of the antenna, in the antennas null. There is a company that makes a filtered line cord that is filtered at the end that plugs into the wall (I do not recall their name and could not find them on a search).
I have a PC that I bought recently that passed with margin when I bought it. However, the last time out it failed. Over the years I have found some of them need to have their shields readjusted after use (the one with the issue is a desktop so it is easy to clean and adjust). In some cases wire ties have failed and internal cables ended up in places they did not belong. There are a lot of items like hubs, switches, USB adapters that are above the limits. So you must be careful on what you are using. Recently I had bought a USB to serial adapter for personal use as it had diagnostic LEDs on it. I used it on a test as it was handy, only to find it was over Class A limits (I guess they did not understand differential pairs). You can ask the list for what what PC's are RF quiet. I am sure there will be a number of responses with current model compliant PCs that you could use. Jim At 08:49 AM 9/24/2008, N.Shani wrote: >All supplier/maker/vendor names withheld in order to protect the >innocent and minimize bias. > >This may have been raised in the past, but I need a refresher and >advice: helping a 3rd party to perform RE testing, and we are seeing >fairly high ambient noise level that is very close to Class B (EUT >is off, only support equipment on) that is in the range of 35-85 MHz >broadband and is coming off the laptops. >The 2 laptops are located outside the AFC and are connected to the >EUT via UTPs running either 100M or 1G traffic from the on-board >Ethernet ports. >Attempts to use a PCMCIA card, desktop PC or dedicated traffic >generator are not showing a better results (it is worse). > >Questions: >1. Is this common? >2. If we add an Ethernet hub, will it help to bring down the noise floor? >3. What are the common tricks used by others to suppress the noise: >ferrites (make, model?) and how many turns, filtered adapters (make, model?) > >Thanks in advance, Naftali - 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/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: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
