Why do my PC and TV images simultaneously wobble?

December 13, 2004 4:48 AM

Strange picture wobble: we have a PC monitor and a television in the same room, and sometimes their pictures wobble in unison. [more inside]

The wobble is not severe but it is noticeable: it is as if every other frame is slightly horizonally displaced. It is most pronounced in the bottom-right corner of each screen, where the degree of wobble can be up to a millimetre on the television. There is a greater degree of wobble when the television is running at 60hz (NTSC) than at 50hz (PAL). The wobble seems more severe on the monitor, which usually runs at 75hz. The television and the monitor are about 2 metres apart. They always wobble together, and the wobble usually persists for about 5 minutes.

I’m convinced it’s something atmospheric, and have been confidently using the wobble to predict impending storms. These storms usually fail to materialise, and my Google skills have failed me, so I have turned to Metafilter to ask: Why do our screens wobble? We live in North-West England, and on the fifth floor, if that helps.

posted by ArmyOfKittens to technology (11 comments total)

A couple questions: What else is plugged into that circuit? Are there any fans nearby? Speakers close to either monitor?

Anything magnetic will literally pull a CRTs picture out from center...so let us know if there is anything in the room that has those polar properties :)
posted by gren at 5:23 AM on December 13, 2004

There are speakers close to both devices: large hi-fi speakers for the telly and little shielded Creative Labs speakers for the monitor. Neither are close enough to their respective screens to do that rainbow thing, though. The hi-fi speakers are a recent addition to the TV, and before their arrival we still got the wobbling.

There are no fans in the room except for the extractor in the kitchen.

There are a whole load of games consoles and DVD players and things coming off the same plug cluster as the PC, but the telly shares a multiplug with the hi-fi and nothing else.
posted by ArmyOfKittens at 5:29 AM on December 13, 2004

The problem is almost certainly either electromagnetic interference or poorly conditioned power. Your first step should be to figure out which one of these is the cause. Try moving one of your displays as far as possible from its current location. Try to keep it away from the walls or other appliances. Try rotating it. Does the wobble change? If so, it's an interference problem.

If that doesn't seem to fit, it's probably a power issue. You can run a test by getting a good quality power conditioning UPS, and plugging one of the displays into that.

If the problem is interference, you need to either move the devices or get some sort of shielding--but then, shielding will probably be too expensive to consider as an option. Alternatively, sell your CRTs and go with LCDs, which are not susceptible to interference problems.

If it's a power problem, complain to the power company and/or use a good UPS.
posted by Galvatron at 5:38 AM on December 13, 2004

I'm guessing that you're picking up a harmonic from some kind of radio transmission. If someone in the area is a amateur radio operator and has a high enough watt system, that kind of distortion can occur. Try looking for an RF filter (they're inexpensive) and see if that doesn't help one of them. The same kind of distorion may occur if you are very close to a cell/microwave transmission towaer, though the odds of an interfering harmonic are a bit more slim. Good luck!
posted by moonbird at 5:41 AM on December 13, 2004

FWIW, I had a roommate that went through a couple of brand new monitors before we figured out the source to his "wobble." He had just received the system and set it up on the outside wall of the apartment. It didn't look good until we discovered the other side of the wall housed every power consumption meter for the building (20+). We rearranged his room to put the monitor on the other side, and all was well.
posted by RobbyB at 5:56 AM on December 13, 2004

If it were interference from the power in the walls it would have to be very strong: the television is directly in the middle of the room, and the nearest wall is made up entirely of window. Unless, of course, they put all the power in the floor, but then we're never getting away from it. Next time the wobble occurs, however, I'll rush and check the TV in the bedroom.

The power thing is kinda believable because our apartment building is two old warehouses joined together, and our apartment is in the brand-new (two years old) bit that joins them; they had to have wired the two buildings together somewhere.

I've just checked on here and we are surrounded by mobile phone towers: I count six within a block. The non-techy gut instinct parts of me have seized on this as a likely explanation.
posted by ArmyOfKittens at 6:18 AM on December 13, 2004

Is there an elevator that passes by? I used to work in Hancock Center on the 38th floor, when the elevators would pass by, the screens in the lab would all do a brief hula.
posted by OneOliveShort at 8:24 AM on December 13, 2004

where are your cellphones during the wobbling?
posted by dabitch at 8:52 AM on December 13, 2004

In my dorm room, our TV wobbles any time the microwave is on. It's about 10ft from the TV screen.
posted by rafter at 10:12 AM on December 13, 2004

All excellent suggestions so far. Here are a few more things to consider.

If there is any low frequency sound or vibrations (infra sound) happening at the same time, for example a machine running somewhere in the building, then the physical movement of the screens will make the images appear to wobble. It has to do with the way the eye perceives the flying spot of light on the screen. (I can even make the picture on my monitor wobble in front of me as I type this by singing a very low note. In this case, it is the vibration of my skull and eyes relative to the monitor that produce the effect, but it is the same process.)

Some people can hear infra sound while many do not. However, you might be able to feel it if you touch the screen very lightly with your finger tips. Should this prove to be the case, you can isolate the monitor/tv with those foam pads they used to put under typewriters.

Rafter, if your microwave is able to influence your tv at that distance I STRONGLY suggest that you clean all around the door seals of the microwave. Trapped food particles which leave small gaps in the door seal can let directed beams escape the machine. Microwaves can resonate within the human skull and produce burns within the brain, which are not felt. This has been studied extensively in the early days of microwaves, especially by the NRC in Canada. (I tried Googling the subject to no effect).
posted by RMALCOLM at 2:08 PM on December 13, 2004

Awesome; thanks for all the ideas. I'll do some experimentation this weekend, and keep an eye out for the disposition of walls, mobile phones, lifts, and so forth the next time it happens.
posted by ArmyOfKittens at 4:30 AM on December 14, 2004