Many years ago at Hagerstown MD, they had a computer (I think it
was an NCR3 or 3000, it's just been too long ago) that at odd
points would just fail. My father was an RF tech working on
radios, and had a contract for the Police Department... so I will
make this short. It turns out that a few stories below this
computer room was the door out of the garage where the police
cars were parked. And so upon exiting the parking garage and
entering the alley to the street, officers would key their mics
to verify their radio was working and that would cause the
computer system to lock up (machine check?).
This was discovered by an NCR CE that had an Oscilloscope doing
tracing trying to find what was causing this problem and just
happened to be standing at the window looking down when a police
car came out and the machine froze..... the police mobile radios
were a harmonic of the system clock!! And were 100 Watts IRC.
A sign was put at the exit of the garage informing anyone who
keyed their mic for their radio before getting out of the alley,
upon being discovered who they were, their pay check would be the
last one to be passed out at the end of the month. This problem
had been invariably happening during payroll runs and they had to
be restarted from the beginning.
Problem stopped.
Steve Thompson
Oh, and the windows did have a metal grid over them in an attempt
to prevent things like this.
On 11/11/2023 5:07 PM, Tom Brennan wrote:
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
<[email protected]> 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, [email protected], 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
<[email protected]> 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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