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Least RF Noisy PC Components

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1RealHope

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Sep 19, 1997, 3:00:00 AM9/19/97

Can anyone recommend any specific models and brands of monitors (15-17 inch
SVGA flat screen styles),
cabinets, keyboards, mice, printers, etc. that broadcast minimal amounts of
RF noise?

I have my desktop on a UPS unit, so I doubt it is injecting noise back into
the AC lines, but my current Vivitron 15 (mfg. for Gateway 2000), and
midi-tower (with M-Tech Motherboard & AMD K6 133) sure kick up lots of
noise!

Also, what about laptops? Any better (RF-wise) than others?

I have an old wooden cabinet am-sw radio (and another with a plastic
cabinet) I'd love to be able to use within less than 6 feet of my PC, and
when I get back into the hobby later in the winter, would like to quiet the
ambient noise level.

Thanks for any advice!
--
Fight for Freedom, Work for Justice, Pray for Peace! DavidC AA1FA

Gary Coffman

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Sep 20, 1997, 3:00:00 AM9/20/97

Your UPS may be contributing to the noise. It is a switcher, and they can
do nasty things to the AC line. As far as the other components, they all
make noise. Often two machines from the same maker have vastly different
noise signatures. So it isn't safe to buy by brand name or model number.
Almost all of them can be quieted, though. It just takes a bit of work.

Monitors are usually the worst offenders. That's because practically none
of them are shielded, and because they use large current spikes in their
deflection circuits, and because they use high frequencies in their video
bandpass. You can't kill those currents or roll off those frequencies without
destroying the resolution of the monitor (or even without screwing up its
sweeps). You have to *shield* the monitor to quiet it. Those spikes and
frequencies are *needed* inside the monitor, your task is to *keep* them
inside the monitor. Standard VHF shielding practices will contain the
noise, and standard common mode suppression techniques will keep it
from getting out on external cables. Copper foil tapes or screen wire will
handle the shielding chores, and ferrite beads over the cables (also shielded)
will deal with the common mode escape routes.

The computer is typically the second worst offender. Again, it has high
frequency pulses running around inside. It *needs* those pulses, they
are your program and data. Your task is to keep them inside. Again it
is shielding which does the trick. Good VHF shielding practice is required.
All openings must be screened, and every seam must have full metal to
metal contact along its length, with a screw every 5 cm along the seam.
Again, all cables exiting the computer must be shielded and equipped
with common mode suppressing ferrites.

Keyboards and mice can be particularly annoying. They are difficult
to completely shield. Of course you can use ferrites on their cords,
but you can't fully shield the keys or the mouse roller area. The best
thing to do here is usually to try several different keyboards and mice
until you find one that's quieter. There's enough unit to unit variation
that this often works satisfactorily. I have found that the Focus 2001
keyboards are generally pretty quiet, and have a good touch too. I
have a bunch of those keyboards in use here. However, *one* of them
was noisy as all get out and I had to discard it.

The one thing which likely *won't* do any good is to "ground" the
computer. That often makes matters worse. All this does is create a
ground loop path for the noise currents, and an antenna (the ground
lead) to radiate them. There is nothing mystical about "ground" which
sucks away noise. Pay attention to shielding and suppression instead.

A note about laptops. Some of them are pretty quiet, some aren't.
They generally use lower voltages and slower clocks than desktop units,
so the noise isn't as pronounced. And they are tightly integrated so there
aren't any long interconnecting cables which can radiate. Beware of plasma
displays, however. They can be real noise generators. And even some LCD
displays can be noisy. Most laptops are in plastic cases to reduce weight, so
their shielding is minimal or nonexistent. And the wall warts they use for
AC supply are usually switchers, and can be *very* noisy. Because of their
size, laptops are often hard to shield and suppress. So if you have a noisy
one, there often is little you can do about it.

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