TV interference problem

[steven017]

I'm having a bit of a problem with interference.

The problem
Basically, when my computer is on, I have interference that looks somewhat like horizontal bars about 4-5 cm wide and made up of what looks like little dots. It scrolls from the bottom of the screen to to top--quite slowly.

It does not affect watching my box too much--the intereference appears less bad when I watch TV through it via S-video. However, watching TV directly via coaxial cable is badly affected. Drives my wife and kids nuts!

The details
I have a splitter connected to my connection on the wall where the service comes into the room. One coaxial cable goes to the VCR and from that to the TV--kids have tons of educational VHS tapes. The other cable goes into a PVR-350. Both the VCR and Sage box are connected to the TV via S-video. Both are also connected to a surround sound system.

When the two cables are connected to the splitter and the computer is on, I get interference as described above. If I connect either cable directly to the service connection, no interference. If I connect one cable to the splitter and NOT the other, I get interference. Seems strange, but true.

One last nugget of info, our TV service is basically antenna. Our area has a large antenna on the mountain that is distributed to all the households in our area.

Current fix
Removed the splitter from the connection and ran coax directly to the VCR. The coax now runs from the VCR to my Sage box. Regular TV tunes via the VCR tuner, which really bites! This setup is way to complicated for me and my family.

Questions
1. Does anyone have any suggestions concerning why this would happen? I mean, if I disconnect my computer from the connection, but connect the splitter to just the coax going into the VCR or TV, I get interference. If I turn the computer off, the interference disappears. Is the splitter picking up RF from my PSU or something like that?

2. How can I fix this? The current situation is unacceptable to us. The splitter is new. Is it just bad?

Steve

[Mitch G]

Yeah, it's probably an RF leak.
If I understand correctly, whenever the splitter is in the path (regardless of whether or not the PC is connected or not) and the PC is turned on, you get interference. If the splitter is not in the path (i.e. the coax is connected directly to the VCR or PC or whatever), you don't see any interference.
So,try a different splitter.


Mitch

[sleonard]

I would suspect something called a ground loop. They are a very common cause of the type of rolling lines you describe.

S

[SHS]

What your seeing is a gound loop
Thing to look for is a Ground Loop Isolator
Jensen Transformers ISO-MAX VRD-1FF
Viewsonics VSIS-EU
The cheapest way
http://www.epanorama.net/documents/g..._building.html

[steven017]

Thanks for the responses thus far.

I appreciate your ideas and help.

It seems to me that at the moment I should try changing the splitter and adding a ground loop isolator. Those are the two suggestions I have received.

In regard to the possibility that the problem is a ground loop, can someone explain how adding just the splitter to the line, but not the cord to the computer, causes the ground loop problem? I'm not sure I follow this, as the interference disappears if I just remove the splitter.

Just so we're clear, here's hopefully a clearer explanation of this particular point. If the splitter is attached anywhere between the service entrance and the TV, but no connection is made to the computer, I get interference. This leads me to the idea that the splitter is picking up RF noise from my computer, which suggests I should try getting a new splitter first.

One other question, when connecting the ground loop isolator, where should it go? Should I put it before the splitter, or should I get two, one for the line to the TV and one for the line to the computer?

Thanks again for the replies,

Steve

[Menehune]

I would first place the isolator in the coax line going to the PC.

In regard to the possibility that the problem is a ground loop, can someone explain how adding just the splitter to the line, but not the cord to the computer, causes the ground loop problem? I'm not sure I follow this, as the interference disappears if I just remove the splitter.

To determine if the problem is ground loop or computer generated interference, is the problem still viewable when the PC is connected to the splitter but turned off? If the problem is only there when the PC is on, it is probably not a ground loop. If the problem is there when the PC is off, it is probably a ground loop.

If you add the splitter without connecting a cable to the second output port, and you have interference, you may have a bad ground on the splitter or a bad patch cord shield connection. Are you using the POS plastic molded push-on RF cable that came with the VCR? Those things are very cheaply made and I have had some bad out of the box. I make my own RF patch cords with SNS connectors and RG6.

I would get a F81 barrel and replace the splitter with the barrel. You can then determine if one of the patch cords from the splitter is letting in the noise.

Make sure the coax screw connections are tight. Use a wrench to gently snug them down.

I would replace parts in this order: the coax cables (preferably make you own with high quality cables & connectors), then the splitter, then add the ground isolator to the coax line connecting to the PC.

Edit:
I used to have a problem similar to yours on an old server (diagonal lines with "sparklies" that slowly moved up the screen-only present when the PC was on). Jiggling the RF connectors alowed me to determine there was a bad shield connection in a cable connected to the splitter. The PC, VCR and TV saw the intererence when the PC was on. Chopping off the bad end, replacing it and tightening the F-connectors cleared up the problem.

[steven017]

Menehune, wow. That was a really good post. I appreciate all the work that went into that.

The interference only occurs when the computer is ON. In any configuration, if the computer is off, I get no interference.

So, I think I will definitely go with the advice to try replacing the splitter and coaxial cables.

The coaxial cables I am currently using include one cable that came with my VCR, one cable for my TV (pretty old now), and one new cable for my computer. All are push on types--this is pretty standard in Japan, and in fact, I can't even recall seeing screw-on types, with a few exceptions (one end of my satellite cable has a screw-on connector -- the one attached to the dish). The funny thing about this is that back home (Canada), I think I could probably say the same thing, but the reverse. I have, however, seen the stuff at the hardware and electronics shops here for making your own cables, so I'll check it out. The may have what I'm looking for.

I will try to get this done in the next couple days and report back.

Thank you very much.

Steve

[steven017]

I'm happy to report that the interference is gone. Here's what seems to have done the trick.

I bought two new cables and a splitter. The cables were ones that were advertised specifically as shielded with shielded connectors. The splitter was advertised as blocking up to 100 db of emi.

After connecting them to my devices, I have no interference. Incidentally, I also eliminated the VCR from the path as my two year old seems to have broken it.

Thanks to all for the advice and help.

Steven