In article ,
Ron Bean wrote:

writes:

I'm looking for a solid desktop (either pizza-box or mini-tower)
computer case that has an all-metal exterior for shielding RFI. This
is for use around radios etc. I realize that SVGA monitors, mice, and
keyboard leak too, but right now I'm looking mainly at the PC box.

I know this is an old thread, but I have a related question:

Quite a few people are building their own PC cases these days--
for example, http://www.mini-itx.com (follow the links on the right side
of the page).

As far as I can see, none of these has *any* RF shielding at all. And I
have yet to hear of them causing any problems (these are not ham radio
operators). The only RF problems I've heard of recently (with consumer
electronics) are microwave ovens interfering with some kinds of cordless
phones.

I'm thinking maybe the only kind of RFI "the masses" are worried about
is TV, and they all have cable...

So I'm thinking of building a computer case for a specific use, and
I'm wondering if I should bother to worry about shielding (evidence
suggests maybe not).



What are you worried about? Ham and short wave fans have a legit
issue, and I guess people doing *very* high quality audio do also.

If you don't fit in a special catagory try taking the top of a
standard PC and hold an AM and an FM radio right next to the running
PC and listen for the noise. You won't hear much. Try it again with
the lid on.

PC cases are built to FCC and European specs for radio emissions. They
are fairly tightly sealed.

The vast amount of emmisions that *do* come out go over all the wires
connected to the PC.

Pick up an ARRL handboox about sheilding and RF interferance
if you want to learn more.

http://www.arrl.org/


--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Just get one of the name brand pc's from a yard sale,
or thrift shop. These cases have paint inside that
helps stop the emi from getting out.

Good quality cables are also a must.

case_dude

(Al Dykes) writes:

What are you worried about? Ham and short wave fans have a legit
issue, and I guess people doing *very* high quality audio do also.

If you don't fit in a special catagory try taking the top of a
standard PC and hold an AM and an FM radio right next to the running
PC and listen for the noise. You won't hear much. Try it again with
the lid on.

I'm not worried about anything specific, but I know the manufacturers go
to great lengths to pass an rfi test, and yet it seems they are solving
a non-problem.

I do occasionally run PCs with the covers off, but I seldom have a radio
or TV on, so if I were causing any interference anywhere (eg in the
apartment nextdoor) I wouldn't notice it. I've heard urban legends about
early microcomputers causing interference, were they noisier or were old
TVs more sensitive to it?

case_dude writes:

Just get one of the name brand pc's from a yard sale,
or thrift shop. These cases have paint inside that
helps stop the emi from getting out.

I would have no problem spending money on a commercially made case, if I
could find one I liked. IMHO, they all suck. Flashy plastic and poor
access even with all the covers off (I didn't consider rackmount cases
because I'd like it to be semi-portable).

I do have one "beige box" here, but I seldom open that one, so I don't
care how awkward it is to mount stuff in it. The other one I frequently
swap out components and I want one that gives me better access with the
covers off. I'm considering a "semi-monocoque" design with no frame.

I worked for weeks to get the RFI out of my computer. It was coming
from within a commerical RFI protected case. I had S-9 plus readings
on 40 and 80 meters. When I finally turned my attention to AC power
cord and filtered it, levels dropped into the normal band noise.

win w0lz

Ron Bean wrote:

I'm not worried about anything specific, but I know the manufacturers go
to great lengths to pass an rfi test, and yet it seems they are solving
a non-problem.

I do occasionally run PCs with the covers off, but I seldom have a radio
or TV on, so if I were causing any interference anywhere (eg in the
apartment nextdoor) I wouldn't notice it. I've heard urban legends about
early microcomputers causing interference, were they noisier or were old
TVs more sensitive to it?


Early PCs had a lower frequency system clock so there were more
harmonics to beat against other signals to cause interference. The
original IBM PC had a 4.77 MHz system clock that caused all kinds of
problems. There wasn't' a TV channel that didn't have at least one
harmonic, and some had two. The interference dropped off as the
frequency went up, but some early computers could wipe out the upper UHF
TV channels.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

Many of the pc power supplies used in the clones
have minimal or no filtering inside them,
once they get the contracts, they strip them down,
eliminate filters and add jumpers to them.


Win wrote:

I worked for weeks to get the RFI out of my computer. It was coming
from within a commerical RFI protected case. I had S-9 plus readings
on 40 and 80 meters. When I finally turned my attention to AC power
cord and filtered it, levels dropped into the normal band noise.

win w0lz