due to some kind of interference, monitor display is "shaking"

Sounds like a large current starts to flow through the cables from electrical power ground to the TV cable ground. This current can cause effect inside the devices/cables and also in some cases the magnetic fields from the cables can carry noise.

Still there is considerable current floating and causign problems. No grounding is ideal.

As such the computer system is working well.

My quess: Your connection of the calbe to electrical ground causes lots of current to flow in the TV cable shield and the electrical power ground wires. This current creates considerable magnetic field in the room and causes problems to your monitor.

In most cases the problem like you can be solved with antenna cable signal isolator and/or better grounding of the TV cable when it enters the house (better grounding together with mains panel ground reduces the potential differences between your electrical outlets and cable TV outlets if your elctrical wiring is done right).

Usually the easiest is to install an antenna cable signal isolator between the antenna outlet and the component that causes problem. In this case all problems related to the shaking most propably would be solved by installing an auitable isolator between your antenna outlet and your surge suppressor. This gets rid of the ground loop.

One potential problem with this setup: The cable modem system might not work well with all of the isolators in the market. Not all antenna signal isolators pass properly the cable modem return channel signals (lower frequency and much higher amplitude than normal cable TV signals).

Here are some links for more information:

First some principles to appreciate the problem. Wire is not a perfect conductor. Electricity on one end is not the same as electricity on the other - minor differences exist. That is why an antenna grounded at the far end will still receive radio signals as its near end. Every ground is different because wire is not a perfect conductor.

You don't know what the source of shaking is; external or internal. Therefore we start with basics. First, every incoming utility must connect to the same ground where it enters the building. That means the the cable, telephone, and AC electric must have a common connection at the earth ground (again, earth ground and receptacle safety ground are electrically different). And again, since wire is not a perfect conductor, the connections from each incoming wire to that earth ground must be short. Code says is must be less than 20 feet.

This ground should eliminate troublesome currents from external sources. Now we are ready to deal with internal sources. Shaking monitor is typically due to magnetic fields generated by large currents inside an adjacent wall or beneath the floor. Moving the monitors may eliminate the shaking by moving monitor away from those magnetic fields.

You have demonstrated that the plug-in protector can contribute to shaking. Well, plug-in protector do not provide any useful transient protection anyway being too close to transistors and too far from earth ground. In fact plug-in protectors can even contribute to damage of adjacent electronics. You require an effective 'whole house' protector on AC electric. And if the cable is properly earthed before it enters the building, then cable is already protected. Eliminating the protector to eliminate the shaking will solve your shaking problem AND not reduce the surge protection.

Learn where AC electric wires travel from ma> hi, I have two monitors connected to my ati card.

Well, I removed the surge protector, and connected the cable which splits to tv card/modem back to wall, and the shaking is there.

the surge protector is not even in use.

IF the cable is not connected to coax on wall, shaking goes away.

I am in apartment, so somewhat limited in what I can do.

thanks for all suggestions.

Actually, it is WORSE Now, after removing surge protector/ground.

Sorry for multiple posts. Just wanted to mention, after removing connection from splitter to tv card on computer, shaking is gone. But now I cannot watch tv:(

Is cable properly earthed where it enters the building to the same earth ground used by AC electric? That is required by National Electrical Code (NEC). However many cable companies have so ill trained their people as to not install this required ground OR connect it to a water faucet which is almost as bad.

Is it possible that your TV has leakage >

Put an antenna cable isolator between the PC TV card and your splitter sould keep the shaking away and still allow you to watch TV.

More information:

Thanks, I will probably get that one from fry's

however, it seems that sometimes there is very little shaking, other times, there is shaking even when no connection to tv card.

any ideas?

I found something at radio shack that says it's an antenna something, and it's coax to coax, but says it is more for tv, and it's $5.99. It's 75ohm. would that do the same thing as what you suggested?

I don't know if this makes sense, but at certain parts of the day, with everything connected(or if i unplug tv), the shaking is bad, but this morning there was little if any shaking, with everything connected?

I can't say. I don't have any Radio Shack anywhere nearby because I don't live in USA. I don't know their current selection other than some checking on their web site sometimes when somebody asks on some specific products. To make any comment I would need more details to be able to find the product description at

The severity of ground lo>

Locate large current wires such as to central air conditioner, electric hot water heater, and electric stove. If that breaker box is in basement beneath the computer and monitor, then numerous circuits in the building may all pass inside wall behind monitor - create substantial magnetic fields. Besides magnetic shielding materials, there would be little you can do except move the system or use a flat screen monitor. Now when do those wires cause monitor shaking? Only when they are conducting large currents. It takes current flow to create those interfering magnetic fields. Only when the electric hot water heater is on will current flow through that water heater circuit.

ok, the thing i bought from radioshack is

The only device that would be effective on the cable was something that galvanically separates the cable from the household appliances. IOW something containing a transformer

- not a filter.

Are you ready yet to deal with magnetic fields generated by underfloor and wall interior electric wires? Minor change was observed when connecting and disconnecting things. That reported nothing useful. A moved monitor created improvement. Why? Classic reasons for a shaking monitor are external magnetic fields or an unstable (and failing) power supply inside that monitor.

Meanwhile, did you verify the earth> yeah, it didn't fix it. does that mean the other suggestion

How close are the monitors to each other? You can have interaction between the electromagnetic deflection, and other wires in the area can change the field strengths. If you are running the same scan rates you can have this problem. If you can change one monitor to another rate and it goes away you need to put something between the monitors to block the magnetic fields. A simple sheet of steel spaced fairly evenly between the monitors can do the trick.

You are right the device that is needed is something that galvanically separates the cable from the household appliances.

Well made galvanic isolation can be made with suitable transformer (need to be carefully deisgned to well cover the whole frequency range used in TV cable without too much attenuation and impedance mismatch).

Other technique used for isolation is to use isolator based on two capacitors. It is kind of speacial hign pass filter on both of the signal wire and the shield. This filter does not pass through any considerable mount of 50 Hz / 60 Hz mains current, but still passes the antenna signals (50-1000 Mhz) nicely.

Both antenna signal isolator types are described in my document at

It is a good idea to check this.

subj:

it could be magnetic: You don't by any chance have a desk fan or another monitor next to the monitor do you :)

I think the surge protector is causing a ground loop in your coaxial and/or mains cable.

to reduce this effect possible move it closer to the service entrance for the electricity and cable. that way the loop will exist mostly outside your dwelling and thefore the electromagnetic effects of it will bereduced.

if it's an atenuator or an ampplifier or a DC blocking module it's not suitable.

A dc blocking module goes half way to the solution by stopping current in low frequency current in the centre conductor. you'd have to modify it by cutting the outer concurtor and installing some ceramic capacitors across the gap. if the unit has a metal case that's not easily opened it'd probably be easier to build an isolator from parts.

Bye. Jasen