ted@imsvax.UUCP (Ted Holden) (07/24/86)
Todd Krein of Dartmouth writes: >Just a question... Have YOU ever tried to make anything TEMPEST class? >It's a hell of lot harder than just a new enclosure, having tried to >do something similar, and having talked w/ people who do it for a living. That's what they'd LIKE you to think, at any rate. I've seen at least one set of blueprints for a tempested device (not a PC) which didn't amount to anything more than placing steel shielding around the inside of the casing for the device. The device in question was more complex than a PC or AT and the system worked. Putting a PC in a metal box would definitely seal off emmisions when you think about it. The mystery to me is why anyone bothers with the other way of doing it (i.e. redesigning boards like ITC does). The pricing of such devices is based on the same logic as the old German fairy-tale about the emporor and his new suit.
caf@omen.UUCP (Chuck Forsberg WA7KGX) (07/25/86)
As I was told, the purpose of the Tempest emissions criteria was to prevent the emission of any energy that would allow the interception of any useful data. A machine could still emit lots of RFI from the CPU clock and power supply without divulging any information. So, a Tempest compliant computer isn't necessarily quiet enough to place next to your neighbor's TV or SW antenna. OF course, since *some* attention has been given to the issue of RF emissions, chances are a Tempest compliant CPU would be cleaner than some others. Chuck Forsberg WA7KGX ...!tektronix!reed!omen!caf CIS:70715,131 Author of Professional-YAM communications Tools for PCDOS and Unix Omen Technology Inc 17505-V NW Sauvie Island Road Portland OR 97231 Voice: 503-621-3406 TeleGodzilla: 621-3746 300/1200 L.sys entry for omen: omen Any ACU 1200 1-503-621-3746 se:--se: link ord: Giznoid in:--in: uucp omen!/usr/spool/uucppublic/FILES lists all uucp-able files, updated hourly
wtm@neoucom.UUCP (Bill Mayhew) (07/26/86)
----Munching line---- Hi, I used to make tempest-proof things for a living. It sure was a heck of a lot easier to make things clean when it was designed in from the ground up. Ground planes on the P.C. board and the like... The most difficult part is attempting to prevent the EMI from escaping through the holes in the case. Obviously, putting the whole thing in a steel box is pretty effective at stopping everthing except very low frequency magetics, but it doesn't do a lot of good for being able to view the CRT. Connectors are also a very nasty proposition, as they allow both conducted and radiated noise to escape, and filtered connectors are enormously expensive. I don't know what was inside, but even little 5 pin connectors cost as much as $100. A few of those replacing $0.29 DB-9s and you can imagine what happens to the price. Screen mesh fronts for CRT faces are also pretty expensive-- at least for the ones that really do stop RF. Computer keyboards are also notorious, and offer a lot of surface holes for emission. A typical solution is to coat the whole set of keys with conductive plastic, which is useful if the thing is going to be used in a jungle any way. One interesting thing is a computer terminal I used, whose main box was pretty much a stock HP 2645 with conductive piant on the inside of the case; the keyboard, however, was a big block of steel with the regular keyboard inside, and the key caps on metal toothpicks sticking in the press the original buttons. Floppy disk drives can also be quite nasty. They're usually dealt with by putting them behind a metal door which can only be opened when the equipment is off. RF-proof air filters can also be pretty exciting. I can't understate how much easier it is to work with things that have been designed from the ground up to be electrically quiet. Keeping noise down in equipment is a fine art that begins with a lot of science. A good case in point are apple computers. I have an early model 2+ that will wipe out a TV clear across the house; I also have a 2e that can sit right next to the TV with negligable effect. The newer case design and PC are really simpler than the old. Bill N. E. Ohio Universities College of Medicine Division of Basic Medical Sciences