"Jan Panteltje" <pNaonStpealmtje@xxxxxxxxx> wrote in message
> If you connect an oscilloscope to for exampel the +5V line, you will
> see it is very noisy indeed, with short spike too.
...and even a power rail that looks exceedingly "clean" on an oscilloscope can
still have plenty of noise riding on it if you start looking closely with,
e.g., a spectrum analyzer!
The manufacturer claiming that the ferrite beads will "improve (the) quality
of the video output
as well as system stability" is undoubtedly overly optimisitic (as others have
stated, the primary for the ferrite beads is for meeting regulatory emission
requirements), although I did once use a PC that had such a noisy power rail
that there was *visible* interface on the video card's output and *some* ISA
cards simply wouldn't operate at all. It was an utterly generic no-name box.
> Normal cases are closed so for RFI to the outside world it should not help.
Actually, unless you're getting a case from the likes of Dell or HP or someone
else with a name to protect, many "normal" cases leak like a sieve. And of
course the current fad in the modding community of putting a large piece of
plexiglass in the side of the case to show off the internals doesn't block
anything below the audio range of EMI. :-)