[sdiy] OT? Shielding a rackmounted computer

[Czech Martin]

Depends on what you mean.

There are ways for interference:

1. electromagetic waves, i.e. higher frequencys where E and H field
are strongly coupled. A sheet of metal will completely damp these,
i.e. : metal case. Depending on the upper frequency limit,
cooling and other openings in the case will have some radiation leakage.
Even for 1GHz the wavelength is 30 cm, so that should be ok.

2. wire bound: this means that the computer distributes currents
into the neighbourhood that in turn will transform into
voltage difference do to ohmic, capacitive or inductive resistance.
This is a big problem if you are connecting not only Midi
(we recently learned about the Midi current loop and grounding)
but also audio. Since all computer cases are grounded to mains
and the plug in cards have signal ground connected to that
this will then lead to massive ground loop problems, not only
hum but also higher sizzle. Switching supply and CMOS processor
says all. A good audio transformer will handle that.
Of course not the individual problem of stray signal allready
inside the sound card.
The mains plug of a computer will also polute his local mains
terminal, i.e. difference voltages may be observed in relatiopn
to other mains ground outlets.

3. Low frequency H or E field.  E field will be tamed with metal
case again, but not H field. I.e.: computer monitor. I think
that flat panel LCDs type screens should have less problems
than the good old CRT. The 40...100Hz vertical scan rate
H field of those is very difficult to shield, it would require
thick sheets of magnetic conductive materials, and how could
you then see the screen?


m.c.

-----Original Message-----
From: Karl Ekdahl [mailto:_nial_ at yahoo.com]
Sent: Freitag, 21. März 2003 18:59
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] OT? Shielding a rackmounted computer


Hello everyone, soon i will include my computer in the
same rack as my musical equipment. Does anyone has any
idea of how to shield the computer (custom built so
any mod is o.k.) so it doesn't interfear with the
other stuff?

Thanks

Karl Ekdahl

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