For the electricians out there:
I recently moved my home office to another part of the house and have
discovered a fairly pronounced symptom of RF interference in my pc
monitor (occassional wavy lines). Unfortunately the optimal placement
of my pc puts it directly above the service panel in the basement and
against the wall where the power enters the house.
I could move my workstation to another part of the room but I'm
wondering if there isn't something I could do to shield first. I must
admit I'm a little concerned about the health effects of this as well.
Thanks in advance,
What you are seeing on the monitor is a low-frequency MAGNETIC flux
field from the power line wireing, not an RF field. Unfortunately,
there isn't any inexpensive and convenient way to shield against 60 Hz
magnetic fields. Distance works, and reducing the field (by pairing
wires) works. Twisting the paired wires helps even more. As a last
resort you might have to buy a shielded monitor - that would be cheaper
than installing shielding for the power circuitry.
First I'd try moving the monitor downstairs and seeing if you can locate
the exact source of the interference. If you have above ground
utilities and the power line isn't twisted where it comes off the pole,
that could be one source.
There is really nothing in a standard computer monitor that would be
susceptible to RF interference unless the signal was so powerful that
sustained exposure would be dangerous to the human body. And there is really
nothing in a breaker panel to generate such RF fields. PCs manage to work
quite nicely in virtually every ham radio operator's station in close
proximity to powerful transmitters where the perceived danger is that the PC
will interfere with the equipment and not vice versa.
I seems more likely that you have an example of magnetic interference. I've
seen this sort of interference before where a computer terminal could not be
operated at a particular desk in a court office without having the image
look like the reflection in a funhouse mirror. I can't remember precisely
what the electrican found when he finally tore into the wall beside the desk
but it was something like poweful currents being returned through a conduit
wall because of miswiring. If your problem is magnetic in nature you should
be able to isolate it by turning off breakers to determine where the current
flow causing the field is located and then work from there. Rotating the
monitor may cause noticeable shifts in the lines. Also, since the
interference is only occasional it might be possible to determine what is
going on in the house at the time of the interference that is causing it.
Let's return to when so many were worried about electricity
causing cancer, et al. So the naive (such as local gossip TV
reporters) put up pictures of high tension power line towers.
Classic of conclusions based only upon speculation. They
immediately suspect it must be those dangerous towers without
first learning simple facts. You now see an example of the
real facts. If AC electric was causing a human health
problem, then you now see where that threat was greatest:
inside house and adjacent to the breaker box where, both,
current is greatest and distance to AC electric conductors is
BTW that electric threat was also promoted using junk
science. Once the original study's data was obtained, then
the conclusion was exposed using flawed statistical analysis.
Monitor is probably suffering from the magnetic fields that
are greatest adjacent to breaker box. Not RF interference.
Magnetic fields. Many expensive solutions exist. A better
alternative is move desk and monitor elsewhere, or maybe buy a
One thing that I forgot to mention before that w_tom brought up is the
possibility of replacing your monitor. If you ditch the CRT monitor and buy
an LCD flat panel you will no longer have magnetic field worries. A decent
LCD can be had for under $500 and while that may seem expensive it is
nothing compared to the cost of buying enough mu metal to shield your
electrical service. Look upon it as an opportunity...
Yeah, well I recently exercised that opportunity when I bought a new
video card that then "required" I upgrade my motherboard/CPU and RAM.
I think I'm tapped out there for now.
Right to all the posters, should've known better. It is magnetic
interference. Thanks for the wake-up.
And thanks for the responses. I hoped it'd be something simple like
tacking some AL foil up over the service panel in the basement (I'm on
the first floor). Guess I better rethink my interior design.
I had a lab at work that had the same problem. Traced it down to the
neutrals and grounds tied together where they were not supposed to be. Check
your wiring and make sure that your grounding is up to snuff, less than 25
ohms. My home which I just tested was less than 5 ohms at the service.
If you are so worried about the health concerns of the magnetic field
then maybe you should stop sitting in front of a pc monitor or a tv or
holding that phone to your head. Oh yeah scrap the micro wave too.
Sorry it just makes me laugh when I hear about the fear of what is
comming out of those big bad electric wires but no one ever worries
about all those devices that they use everyday that consume electricity
In my experience as a computer technician and consultant, the service
panel wouldn't be an issue, but the power line entering the house *may*
be. Remember that a wire creates a tubular magnetic field around it,
whereas a service panel with all its different connections would have a
more diffuse and less focused effect. It's the wires and their
antenna-like effects you have to watch out for.
But I'd expect the actual placement of the monitor and computer power
cables, and the video cable itself, as more likely sources of any
problems. Make sure that none of these wires cross or pass too near each
other, and especially that there isn't one too near to the rear of the
monitor, where the magnetic TV tube is located. Experiment with
different positions. In *rare* cases you may want to place the monitor
on a power strip leading to a separate receptacle, or use a surge
suppressor with isolating receptacles.
At last resort, try moving the monitor to another part of the room. If
need be place a dark blue field on the screen and move the monitor
around to see what effects you can notice.
Actually, a last resort would be switching to a better monitor, or an
LCD screen (unless you're a hardcore gamer).
Shielding is both easier and more difficult than you might expect.
Creating a simple Faraday cage between your monitor and the power lines
could be as simple as some chicken wire against the wall (you can
conceal it behind anything). But completely isolating yourself from
interference can be a black hole of maybe this, maybe that trial and error.
The Faraday effect is why buildings with metallic structures can
interfere with cell service, even if they have plenty of windows.
Statistical studies show a weak to nonexistent association between power
lines and cancer:
There was enough concern in the 80s to lead to thousands of studies
worldwide (in other words, it wasn't just a media scare; there were
concerned scientists as well), but fortunately, few were able to
demonstrate any considerable and consistent danger. The one that is
still considered widely applicable is use of old-style computer monitors
by pregnant or potentially pregnant women (especially when they sit
*behind* a monitor rather than in *front*, as in some secretarial or
call center pools), but monitor manufacturers have followed the strict
Swedish guidelines for around a decade now.
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