Don Borowski at Schweitzer Engineering Labs wrote:
>> Loading up the PCI slots puts more capacitance on the PCI bus, slowing the logic transistions and thus reducing emissions. Quite likely loading up the ISA slots will do the same thing, though emissions could go up.<< Some years ago, a computer product I worked on generated a terrible 105 MHz emission. This was without too much trouble traced to the unterminated ISA bus, which was resonant in that range; the bus drivers were tri-stated to save power, and only turned on when a signal was detected, but the resulting high impedance allowed noise to thereby trigger oscillation at the bus resonant frequency. As soon as a card was inserted, things quieted down. An aside: Had we tested this only with the maximum configuration we would have missed the problem - but 5 volts in the FM broadcast band would surely have come to our notice later! Cortland Cortland 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
