At 20:44 3/18/98 -0500, you wrote:
Standard UPS's do not operate with their batteries "on-line" but in standby mode. Because of this you do not get any of the filtering affect from the batteries. You can get good "online" UPS's with gel-cell battery banks but they cost $$$. Look at some of the companies that service the telcom industry providing UPS for switchrooms. Line conditioning on the standard UPS's (PC Decsktop grade) is medeocere at best and are designed for leveling out power fluctuations not for filtering data leakage.
If Tempest is a serious concern I recomend a dual battery bank so one bank can be charging while the other is in use. Physicial disconnects on both battery banks between the computer and between outside power grid to insure physicial issolation durring operations.
While I agree with you in that total security is only possible if you completely isolate the system, I think that the original person posting wasn't referring to the batteries, but rather the conditioning that is going on inside the UPS. Any decent ups will put the incoming power through a "conditioner" that will filter out noise in the incoming power, and rebuild the wave so that transient sags and spikes don't get through. It stands to reason that these filters would work in reverse, since they are AC filters. Most AC circutry works equally well in reverse as forward. DC circuitry would probably filter out noise equally as well since it simply won't work in reverse for the most part, it'll simply resist any reverse current until it blows. Of course, I make no claims about noise that the transformer itself may make while it does it's filtering that someone might be able to use to determine what was filtered out. -The Spectre [SP4 w/ Clam Cluster] -http://www.anthrax.net/cos "No man is clever enough to know all the evil he does." - La Rochefoucauld