Interference from A/C on my monitor

[mallowman]

It seems that the window unit air conditioner in my room (and possibly the one on the other side of the wall behind my computer) cause interference with my monitor. When the compressor is running (just the fan is okay) the image on my screen gets a little wavy and unstable. Does anyone have any idea what I can do about this? I've thought about maybe a dirty power signal, but they're on a different circuit and I've got a UPS which as I understand it conditions the signal anyway. I also thought about putting additional ferrite beads on the signal cable, but I don't know if that will help any.

[Gurm]

You know, I have that problem as well. It's the wiring in my house. Despite being behing a UPS/Conditioner, it happens anyway. REALLY pissing me off.

- Gurm

[LvR]

"Ferrite beads" wont help I suspect as the interference is most likely caused by the relatively slow varying (50 or 60Hz) stray magnetic fields generated when the high current compressor motor does its thing.

It interacts with the monitor by affecting the shadowmask and the actual metal parts of the casing, as well as directly with the path followed by the electron beam on its way to the front of the screen.

Easiest solution is to relocate the monitor.

WoW solution is to have a Faraday-cage (that kills any stray magnetic fields before it can interact with the monitor) constructed around your monitor.

Try another brand of monitor - I have often found that construction techniques includes an integrated mini Faraday-cage made of metal shielding plates around most of the tube neck area.

If you cant change the location of the monitor, the only alternative is to change to a non-magnetic based display technology - eg - LCD etc

[mallowman]

Thanks for the information, the thing I still don't get is that I've had this monitor even closer to the A/C unit in my room and hadn't noticed it before. I've also noticed that the intensity of the effect varies with the refresh rate I'm using.I don't suspect that building a cage around the monitor would work out since I sit between the monitor and the A/C unit. Could it be the extra current going through the wires in the wall when the compressor is running since the computer wasn't up against this particular wall before.

[LvR]

Proximity to the source of the problem is only part of the equation. With magnetic interference the actual orientation relative to the field lines is a huge thing as well - thats why re-orientating the monitor often changes the severity of the effect.

Your refresh rate will cause a "beat pattern" like you are finding if the refreshrate is exactly or close to a multiple of the ac powersource frequency.

I don't suspect that building a cage around the monitor would work out since I sit between the monitor and the A/C unit

Wrong - your body is most certainly not made of metal. It was also suggested only as a really way-out solution and is often only a viable thing to do in a lab/research fascility.

Could it be the extra current going through the wires in the wall when the compressor is running since the computer wasn't up against this particular wall before

Most defenitely - ANY conductor carrying a current generates a magnetic field around it that may influence/interfere with equipment .

Modern electrical installation practices now also allow the installation of power cables in PVC tubing iso metal tubing - guess what that tubing were able to do for us in the past?

[Agent31]

LvR, I quite agree, it's more likely to be magnetic interference.

RF interference will cause static like you'd get if you were vacuuming near the TV, you'll get that from any high-frequency electrical motor, but the wobbly business kind of indicated a lower frequency. Short of building yourself an EM bouncing box so you can fry yoursel with all your EM from the monitor and keep out the magentic interference, you'd be best just shifting the monitor around a bit, or buying a pair of those novelty coke bottle glasses

[The PIT]

I've got one monitor in my room that does the same thing intermittantly. Nothing else in the room maybe on but you get a shimmering. I can ponly presume it's something in the neighbours house.

[mallowman]

Wrong - your body is most certainly not made of metal. It was also suggested only as a really way-out solution and is often only a viable thing to do in a lab/research fascility.

I meant in that if there were a cage around the monitor I wouldn't be able to see it. Guess I forgot the smiley, oh well.