Re: PC Interference from shredder Was: Kinda fun

[Tom Brennan]

Just before I worked with mainframes I drew maps on a computer that had 
a big display, a small drawing pad and pen, and a large light table with 
a "puck" for tracing existing maps into the computer.  Both the puck and 
pen worked by receiving a magnetic signal from the pad or table in order 
to determine its location.  About once a week someone would complain 
that their pen was throwing the cursor all over the screen, so a new pen 
was ordered at maybe $500.

The light table had bunch of fluorescent bulbs inside, and you could dim 
them with a knob if needed.  One day I noticed that when the light was 
either full on or full off, there was no problem with my pen.  But if 
the dimmer was in the middle, the pen had issues.  Those dimmers used 
triacs which work by holding back each AC wave a bit and then sharply 
rising.  The sharp rise generates all sorts of EMF and that's what was 
messing with the coil in the pen.

On 11/11/2023 12:55 PM, Wayne Bickerdike wrote:
On the subject of RF interference. Years ago we came back from living in
California to Australia. We had a 110V coffee espresso machine. It worked
well and we ran it from a voltage changer plugged into the socket. Early
rise time, my wife would go into the kitchen and make a coffee.

I'm in the habit of reading my email and surfing at that time (like now in
Australia).

For weeks and months my internet would go off and come back a few
minutes later. I eventually tied it back to the coffee machine/voltage
reducer. We stopped using it and all good. The wireless router runs on
2.4Ghz and is located in my study, maybe 30 feet from the kitchen and there
is a double brick wall in the way.

As an adjunct to this. I switch off my router at midnight and I get much
better sleep.

On Sun, Nov 12, 2023 at 6:11 AM Joel C. Ewing <jce.ebe...@cox.net> wrote:

I think shielding of the PC itself is unlikely the problem, unless the
case is not properly closed.  All PCs I have ever seen have metal cases,
which if properly seated and grounded act as a RF shield, inbound and
outbound.

Any electric motor could be producing power transients at power on/off
and possible RF interference from contact arcing (which can increase
with motor age), which might travel over the house wiring, or via air
and get picked up by other cables in the room which are connected to the
PC.  Any magnetic effects of a motor should be minor by comparison.

If it's a large enough motor, start up may produce a temporary dip in
voltage big enough to be a problem for a computer that is not powered
through an Uninterruptible Power Supply (UPS).  If you notice any lights
flicker when the shredder powers up, that definitely could be an issue.
If you are not already using a UPS for your PC, you probably should be,
for other reasons as well. The shredder definitely should not be plugged
into the same outlet as your computer, and it would be best if it were
on a different house circuit as well.

If the problem only started occurring after adding RAM, maybe the PC
power supply is now working harder making it more sensitive to power
dips than before.  It's also possible the computer may be getting old
enough that the power supply is getting less effective at filtering out RF.

If for some reason the shredder motor is broadcasting more RF
interference than in the past, keeping it further away from any cables
connecting devices to the PC may help.  There are also some relatively
inexpensive ferrite beads that can be clipped onto cables near the
computer to block RFI from entering via that route.

Assuming you are in a house, the simplest experiment is to try moving
the shredder to another room far away from the PC where it can be
powered from a different house circuit.  If that eliminates the problem
and having the shredder in a different room is acceptable, moving the
shredder away from the PC may be the simplest short-term solution.
Otherwise you can either try using a UPS for the PC and/or adding
ferrite RF filters on PC device cables that don't already include a
filter, especially if there are any cables that are routed close to the
shredder.

      JC Ewing


On 11/11/23 06:34, Bob Bridges wrote:
Hah!  A few years ago I had my hardware-geek son build my latest tower
PC.  It's pretty good - not water-cooled like the one he made for himself,
but a nice big monitor and I finally gave him permission to load me up on
RAM.  But ...

Do normal commercial PCs have Faraday cage around them, or something?  I
can't use my old paper shredder any more, because when it fires up within
the same room, the PC suddenly dies and has to be rebooted.  A minor EMP, I
take it.

---
Bob Bridges, robhbrid...@gmail.com, cell 336 382-7313

/* The will to win is not nearly as important as the will to prepare to
win.  -R.M. Knight */

-----Original Message-----
From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On
Behalf Of Leonard D Woren
Sent: Saturday, November 11, 2023 02:12

Long ago I was told why my shop didn't carpet the tape storage area.
Apparently some shop that did had a problem with unreadable tapes.
Eventually they figured out that all the unreadable tapes were on the
bottom row of the tape storage.  And the outside cleaning people used a
vacuum cleaner...

--- Bob Bridges wrote on 11/8/2023 6:56 AM:
/* The more sophisticated the technology, the more vulnerable it is to
primitive attack. People often overlook the obvious.  -Dr Who, 1978 */

--
Joel C. Ewing

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