Take a closer look at some of the higher quality cases.

All the cases I have purchased within the past few years have plastic, as
you say, over the drive bays, but there is metal behind that plastic. If
you want to use the bay you need to pop out the metal. Except for floppies,
the drives generally have metal behind their plastic faces, too.

More important is the scheme for attaching the sides. Those little drive
holes will let some RF out, but long, narrow gaps in the side let out a lot
more. Most recent cases seem to have fairly elaborate schemes to be sure
that the sides don't leak.

I can't believe many of the mass marketed cases actually make it to
manufacturers who need to be certified, but the lengths they go to ensuring
RF shielding lately would indicate to me they are getting pressure from
somewhere.

As best I can tell, the case isn't nearly the problem the wires are, but
even there, it seems like the newer stuff is pretty well behaved. My
radios are pracically surrounded by computers and no noise anymore. Used to
be a real problem but as the computer equipment has gotten newer, the
interference problems have faded. I can still hear my Ethernet on some
bands, but I have a pretty ancient hub. Once that gets replaced I suspect
the ethernet problem will disappear, too.

...

xpyttl wrote:


Don't forget to throw some toroids on your cabling. I have a whole bunch of
2" cores I keep around just this purpose. My wifes machine threw out a lot
of QRM. Cheap case and power supply (though all-metal). Wrapped the cord
twice around a core and poof! QRM gone.

--
Visit the new Unlicensed QRP website and forums: http://www.qrp.timpauly.com
The site and forums are geared toward legal, unlicensed (non-ham) radio
operation for low-power hobbyists around the world.

On Sun, 15 May 2005 12:28:21 -0700, "John Smith"
wrote:

Personally, I'd place a sheet of aluminum window screen between the acrylic
sheet and the case--that way I could still get the effect of looking into
the case, and still be shielded...

Other than that, I'd pick the one from their catalog which DOESN'T have the
"big gaping hole" in the side... grin

FYI:

Some plastic used in cases has a "flash" coating of aluminum
(sputtered in a vacuum chamber). While the metal is extremely thin,
just a few microns, it is enough to provide RFI shielding.

Obviously not as good as solid metal for shielding, but good enough
for many uses. Check out what sort of plastic before assuming it will
not shield.

Happy trails,
Gary (net.yogi.bear)
--
At the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

In article .com,
Tim Shoppa wrote:
They make 'em: http://www.directron.com/pc75.html

What about that gaping big square-foot hole in the side?

I have even seen an all stainless steel case which is used around
food

The old "PC Power and Cooling" all-metal-tower used to be good (I think
it was available in chrome!), but they don't sell them anymore
(probably because they cost several hundred $).

I'm not looking for anything particularly stylish. Just a case without
big holes covered by plastic.

Tim.



If you buy a brand name computer it meets some prety good FCC specs
for emission. IMO if you are carefull any good all-metal case will
produce an EMI-tight case.






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

Don't blame me. I voted for Gore.

xpyttl wrote:

[Good hints about where to look for shielded cases,
esp. related to FCC standards]
[...]
the case isn't nearly the problem the wires are

This is very true. A typical SVGA copper cable puts out all sorts of
hash (as well as the monitor!). And lotsa junk is radiated and
conducted out by the power supply cable, even for the "best of the
best" PC clone supplies.

I've discovered and/or engineered some workarounds, consisting of going
to optical fiber instead of metal whenever possible. But my converters
are usually outside the PC case so this doesn't completely eliminate
the radiation from copper cabling.

I'm starting to think I should just sit inside the Faraday cage with my
computer, and put all the radios outside!

Tim.

In article .com,
Tim Shoppa wrote:
xpyttl wrote:

[Good hints about where to look for shielded cases,
esp. related to FCC standards]
[...]
the case isn't nearly the problem the wires are

This is very true. A typical SVGA copper cable puts out all sorts of
hash (as well as the monitor!). And lotsa junk is radiated and
conducted out by the power supply cable, even for the "best of the
best" PC clone supplies.

I've discovered and/or engineered some workarounds, consisting of going
to optical fiber instead of metal whenever possible. But my converters
are usually outside the PC case so this doesn't completely eliminate
the radiation from copper cabling.

I'm starting to think I should just sit inside the Faraday cage with my
computer, and put all the radios outside!

Tim.



They "lumps" found on many power and data cables are ferrite cores
that attenuate the RF hash that leakes out on the conductors.
Building an RF-proof case is trivial if you don't need any
peripherals. RF comes out on the wires.

Look at a copy of the Ham Radio _The ARRL Handbook for Radio
Communications_, in any decent library or bookstore. They cover RFI
solutions.

Do you have an EMI problem ?







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

Don't blame me. I voted for Gore.

In message .com, Tim
Shoppa writes
xpyttl wrote:

[Good hints about where to look for shielded cases,
esp. related to FCC standards]
[...]
the case isn't nearly the problem the wires are

This is very true. A typical SVGA copper cable puts out all sorts of
hash (as well as the monitor!). And lotsa junk is radiated and
conducted out by the power supply cable, even for the "best of the
best" PC clone supplies.

I've discovered and/or engineered some workarounds, consisting of going
to optical fiber instead of metal whenever possible. But my converters
are usually outside the PC case so this doesn't completely eliminate
the radiation from copper cabling.

I'm starting to think I should just sit inside the Faraday cage with my
computer, and put all the radios outside!

Tim.

Have you tried unplugging the PC from the mains?

--
Jeremy Boden

I recently purchased a Mac Mini G-4. Quietest computer I've ever owned. I DX
mostly BCB, and I can point my KIWA loop directly at the box (about 3.5 feet
of separation), and there's no noise. The flat panel monitor causes some
hash, but I simply put the Mac to sleep and the monitor shuts up. Get a Mac!

--Guy
Thurston, OR


On 5/16/05 5:42 AM, in article , "Jeremy
Boden" wrote:

In message .com, Tim
Shoppa writes
xpyttl wrote:

[Good hints about where to look for shielded cases,
esp. related to FCC standards]
[...]
the case isn't nearly the problem the wires are

This is very true. A typical SVGA copper cable puts out all sorts of
hash (as well as the monitor!). And lotsa junk is radiated and
conducted out by the power supply cable, even for the "best of the
best" PC clone supplies.

I've discovered and/or engineered some workarounds, consisting of going
to optical fiber instead of metal whenever possible. But my converters
are usually outside the PC case so this doesn't completely eliminate
the radiation from copper cabling.

I'm starting to think I should just sit inside the Faraday cage with my
computer, and put all the radios outside!

Tim.

Have you tried unplugging the PC from the mains?

Tim Shoppa wrote:
xpyttl wrote:

[Good hints about where to look for shielded cases,
esp. related to FCC standards]
[...]
the case isn't nearly the problem the wires are

This is very true. A typical SVGA copper cable puts out all sorts of
hash (as well as the monitor!). And lotsa junk is radiated and
conducted out by the power supply cable, even for the "best of the
best" PC clone supplies.

I've discovered and/or engineered some workarounds, consisting of
going
to optical fiber instead of metal whenever possible. But my
converters
are usually outside the PC case so this doesn't completely eliminate
the radiation from copper cabling.

I'm starting to think I should just sit inside the Faraday cage with
my
computer, and put all the radios outside!

Tim.

Tim,

You are really close to your own answer. I built a Faraday cage area
around my laptop. And also plugged into a surge/noise filter for
the AC and use metal hood cables to hook up to the radios.
I hardly experience any noise at all.

The reason is most manufacturer are turning to plastics and putting
less and less shielding in them. Keep in mind the OEM's are building
for the general public.

Bruce

Jeremy Boden wrote:

What band does a PC broadcast on?

It leaks on wide range, with peaks varying on different PC's. You can
certainly hear it clearly enough bringing an AM radio near your
computer.