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

J

John H.

Jan 1, 1970
0
hi, I have two monitors connected to my ati card.

I have
coax on wall - > cable modem surge protector (very small
-> 2- way splitter -> cable modem
-> tv card on pc

there is a line off the surge protector which goes into screw
in order to ground it.



OK, so there are several weird situations from this. If I have
coax from splitter to TV card, and I do not ground it to wall
outlet, both monitor displays shake REALLY heavily. If I ground
it to wall outlet, large 19 inch CRT shakes some, but not nearly
as much(where I am at now).

Now, if I move computer and two monitors to other side of room
with no peripherals attached, no shaking. If I simply plug the
surge protector into the coax on this side of the room, and ground
is connected, even though NOTHING Is connected to surge protector,
on the clear other side of the room, both monitors begin shaking!

I need a way for everything to live in harmony:( The shaking,
even though it is minor right now, is mild, but still too much:(
I know a lot about computers, but not too much about electronics.
How can I get rid of ALL shaking?

thanks!
 
T

Tomi Holger Engdahl

Jan 1, 1970
0
John H. said:
hi, I have two monitors connected to my ati card.

I have
coax on wall - > cable modem surge protector (very small
-> 2- way splitter -> cable modem
-> tv card on pc

there is a line off the surge protector which goes into screw
in order to ground it.



OK, so there are several weird situations from this. If I have
coax from splitter to TV card, and I do not ground it to wall
outlet, both monitor displays shake REALLY heavily.

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.
If I ground
it to wall outlet, large 19 inch CRT shakes some, but not nearly
as much(where I am at now).

Still there is considerable current floating and causign problems.
No grounding is ideal.
Now, if I move computer and two monitors to other side of room
with no peripherals attached, no shaking.

As such the computer system is working well.
If I simply plug the
surge protector into the coax on this side of the room, and ground
is connected, even though NOTHING Is connected to surge protector,
on the clear other side of the room, both monitors begin shaking!

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.
I need a way for everything to live in harmony:( The shaking,
even though it is minor right now, is mild, but still too much:(
I know a lot about computers, but not too much about electronics.
How can I get rid of ALL shaking?

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:
http://www.epanorama.net/documents/groundloop/index.html
http://www.epanorama.net/documents/groundloop/home_solving.html
http://www.epanorama.net/documents/groundloop/antenna_isolator.html
http://www.epanorama.net/documents/groundloop/antenna_isolator_building.html
 
W

w_tom

Jan 1, 1970
0
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 mains (breaker)
box to everywhere in the house. Especially 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.
 
J

John H.

Jan 1, 1970
0
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.
 
J

John H.

Jan 1, 1970
0
Actually, it is WORSE Now, after removing surge protector/ground.
 
J

John H.

Jan 1, 1970
0
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:(
 
W

w_tom

Jan 1, 1970
0
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 into its antenna?
Or that the polarized plug is not properly connected?
 
T

Tomi Holger Engdahl

Jan 1, 1970
0
John H. said:
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:(

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:
http://www.epanorama.net/documents/groundloop/home_solving.html
http://www.epanorama.net/documents/groundloop/antenna_isolator.html
http://www.epanorama.net/documents/groundloop/antenna_isolator_building.html
 
J

John H.

Jan 1, 1970
0
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?
 
T

Tomi Holger Engdahl

Jan 1, 1970
0
John H. said:
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 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
www.radioshack.com and then make my judgement woudl this
product sound as right for this or not.
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?

The severity of ground loop induced problems can vary over time.
I have seen this. In many situations the severity of the problems
is related to the load of your house electrical system, or if
some specific equipment are turned on or not. In many cases the
ground potential differences tend to vary more or less depending
on how the electrical power system is loaded inside the house.
 
W

w_tom

Jan 1, 1970
0
John H. said:
...
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?

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.
 
J

John H.

Jan 1, 1970
0
ok, the thing i bought from radioshack is
75-ohm tv/vcr/fm interference filter
????
 
J

John H.

Jan 1, 1970
0
yeah, it didn't fix it. does that mean the other suggestion
for device wouldn't either?
 
W

w_tom

Jan 1, 1970
0
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 earthing of cable, AC
electric, etc to a common earth ground at the service
entrance? That is even required by code AND often violated by
cable companies who hire on price rather than on technical
knowledge.
 
T

Tomi Holger Engdahl

Jan 1, 1970
0
w_tom said:
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.


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
http://www.epanorama.net/documents/groundloop/antenna_isolator_building.html
Meanwhile, did you verify the earthing of cable, AC
electric, etc to a common earth ground at the service
entrance? That is even required by code AND often violated by
cable companies who hire on price rather than on technical
knowledge.

It is a good idea to check this.
 
J

Jasen Betts

Jan 1, 1970
0
subj:

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

Jasen Betts

Jan 1, 1970
0
hi, I have two monitors connected to my ati card.

I have
coax on wall - > cable modem surge protector (very small
-> 2- way splitter -> cable modem
-> tv card on pc

there is a line off the surge protector which goes into screw
in order to ground it.

OK, so there are several weird situations from this. If I have
coax from splitter to TV card, and I do not ground it to wall
outlet, both monitor displays shake REALLY heavily. If I ground
it to wall outlet, large 19 inch CRT shakes some, but not nearly
as much(where I am at now).

Now, if I move computer and two monitors to other side of room
with no peripherals attached, no shaking. If I simply plug the
surge protector into the coax on this side of the room, and ground
is connected, even though NOTHING Is connected to surge protector,
on the clear other side of the room, both monitors begin shaking!

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.
 
J

Jasen Betts

Jan 1, 1970
0
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?

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
 
J

Jasen Betts

Jan 1, 1970
0
ok, the thing i bought from radioshack is
75-ohm tv/vcr/fm interference filter
????

I think those are to block HF CB-radio signals, it's unlikely that such a
device will help.

those URLs look promising.
 
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