Gary Collier wrote in a message to Michael Welch:
 GC> I am temporarily utilizing an old(metal)IBM Brand XT type 
 GC> chassis case to hold my AT MB. It has a 230W PS, and works fine 
 GC> except that it has limited space for two floppy or CDROM 
 GC> drive/floppy. The main problem I have is the high RF disruption 
 GC> of the Television screen...(15 feet away).
 GC>        1) what is the cause of this RF? 
Most computer innards have components that switch very sharply from one 
voltage level to another at a fairly high rate of speed.  This means that not 
only are those frequencies present,  but also lots of harmonics of higher 
order,  way up there.  If you did an energy vs. frequency plot it would look 
like a picket fence,  sloped.
 GC> Is it the power supply?? 
It's possible that the power supply also contributes to this problem,  though 
I doubt very much that it's the primary cause.
 GC> Is it the metal case?? 
The metal case will no doubt have *some* sheilding effect.  It's not perfect, 
 and the problem is going to be aggravated by any cables coming out of that 
case.  That's why in a lot of instances you see ferrite beads on things 
(usually covered with plastic,  but that's what they are).
 GC> Is their anything that can be done? 
Yes,  you can make sure you've got the best quality shielded cables that you 
can manage,  that they each have ferrite beads on them,  that *all* screws 
holding the case together are present,  and similar stuff.  It's a bit of a 
black art,  trying to deal with this stuff.
The other thing I'd suggest is that you get the antenna for your tv elevated 
and as far away from the computer gear as possible.  The better the signal 
the tv has to work with,  the less noise you're going to see.
 GC> My plastic case didn't have as severe a problem but nonethe 
 GC> less has some deletorious effect. 
I've not encountered too many plastic cases for computers,  but the ones I 
have seen were usually sprayed on the inside with a material that was 
supposed to act as a shield.  Osborne cases come to mind as one example.
 GC> If I went to D.C. , would it decrease? 
Probably wouldn't make much difference,  it's not the power source so much as 
the nature of the beast.
 GC>        2) How would RF be affected in an RV type use. I am 
 GC> contemplating placing a MB in the base of a wood(multi-purpose) 
 GC> RV TV type cabinet, with a large computer fan venting through 
 GC> the wall or into the "basement" of the RV to muffle sound. 
You'd do well to look into conductive sprays for the inside of that plastic 
case (which would have to be "grounded" somewhere or other) or perhaps some 
metal screening that could be applied to the inside of it.  Again,  a good tv 
antenna as far as possible from the computer should help.
 GC> Are longer IDE cables made for connecting floppies or wouild I 
 GC> have to hack one?
They're out there,  usually made for tower cases (and I could use one here as 
a matter of fact :-).
If you have a problem finding one talk to someone that does a lot of stuff 
with networks,  they are usually the folks using the bigger cases.
 GC> Is their any more of a fire hazard with wood rather than with 
 GC> those ugly flymsy plastic cases?
Not that I can see.
email: roy.j.tellason%tanstaaf@frackit.com 
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