Greetings all, At a former job, I actually performed many scans of LCD monitors from many 'unnamed' manufacturers and found them to be "different" from normal CRT's for emissions purposes. The LCD's would incorporate fast (for monitors) clocks for processing. I have seen clocks anywhere from 65 to 140MHz in these monitors. Needless to say with the cost-cutting involved with mass-production, these production monitors were almost always very close to if not over the Class B limits. (Keep in mind I was not performing the scans for the initial manufacturers, so I doubt anything changed because of my results). The emissions peaks were narrowband harmonics of the clock instead of the more random seeming Scrolling H's noise that is typical for CRT monitors.
For that matter, I NEVER saw a CRT monitor that passed class B with HHHHH's scrolling at a high resolution (BTW, the scrolling H's pegs the PC processor as well). As these monitors were almost always support equipment, the typical "fix" was to run the scrolling H's in a DOS window and then ALT-TAB to a full-screen dos window. This greatly reduced the resolution, refresh rates, etc sufficiently to make the monitors very quiet. Hope this helps (and that my memory is correct) Dave George Stults wrote: > > Hello All, > > I have theorized that a Liquid Crystal Display (LCD) monitors should have > less radiated emission than a comparabe CRT (same viewing area) since there > is no high voltage tube and high powered oscillators, etc. I am wondering > if anyone can confirm or deny this rumor based on actual testing. Also If > there are folks in the crowd who sell LCD monitors, I would like to hear > from you offline. ------------------------------------------- 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: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
