You'll get the same effect if you hold your mobile phone next to your
monitor when it's transmitting - as on a call .
Depending on the particular monitor anyway. I have a 15" monitor which is
very susceptible, but my 17" doesn't bat an eyelid.
If the scan is being modulated then it's a sort of rf ( 15625 is rf ) and
not anything to do with degaussing. Degaussing only occurs at switch on
.Possibly your old monitor has got line output fundamental or harmonic
components which are radiating and getting into the line drive stages of the
other monitors, thus causing the continuous ripple - effectively a " beat
note " on the drive waveform.
Thinking further, as it's an old monitor it probably puts out a lot more rf
than a modern monitor due to the "possibly " lower efficiency of the drive
ccts.
Geoff.
----- Original Message -----
From: "chris" <cb_at_mythtech.net>
To: "General Discussion: On-Topic and Off-Topic Posts "
<cctalk_at_classiccmp.org>
Sent: Tuesday, June 01, 2004 6:03 PM
Subject: Re: OT: CRT EMI Shield
> >I wonder if degaussing the target monitor (one with interference),
> >while the source monitor (creating the interference) was operating, would
> >help?
> >
> >Some monitors have a built in degaussing function.
> >Others do it when they power up.
>
> Nope, doesn't seem to make a difference. (one of the two distorted
> monitors has a degaus button, the other I believe has a built in degauser
> and I tried power cycling that one. Neither saw any change).
>
> >The above all assumes a magnetic interference.
> >If it's localized to one, or a few, spots on the screen, with color
shifts,
> >that's likely what it is.
>
> What happens is, the image on the monitor on the bottom starts wobbling
> and bouncing. And the scan lines become very pronounced. The monitor to
> the side flickers and wobbles a bit.
>
> This only happens when the top monitor is turned on and "charged" (when I
> first turn it on, there is about a 1 second pause before you hear the CRT
> charge, during that pause there is no distortion). I can remove the
> distortion by simply turning off the top monitor. Also, moving it about a
> foot away gets rid of it as well (so worst case, I can install a shelf on
> the wall a little higher up. Right now its sitting on a plastic monitor
> shelf that rests directly on top of the monitor below).
>
> I'll see if I can try a newer, possibly better monitor as the top one and
> see if the problem goes away (the one I picked to use is an older
> monitor. Since it will not be used too heavily, I didn't want to
> sacrifice a good monitor... but I'd rather have no problems then save on
> a good monitor)
>
> >Of course that gets me to thinking of TEMPEST and someone reading your
> >monitor from out in the street. :-)
>
> Humm... well, unless they are turning on and off their equipment at the
> exact same time I turn on and off the top monitor... it seems unlikely.
> Of course, if the screens are seeing this much distortion, I'm curious
> what the 4 CRTs pointing at my chair is doing to my brain!
>
> -chris
> <http://www.mythtech.net>
>
Received on Wed Jun 02 2004 - 18:11:48 BST