Possible Power quality problems with cable company signal 1

[MrJam]

Recently A cable company ask use to do some power monitoring at a few of there subscribers houses. Apparently, their having trouble with the television picture tiling, or pixelating in these houses. They have tried everything they can think of. The company thought that it might be a power quality problem. I thought maybe ferrite cores on the coaxial cable might help. We are setting up a Hioki 3196 on the power lines coming into one of the houses to give us some insight into the problem. Does anyone have any possible solutions

 

[jghrist]

I'm no expert, but when my digital tv picture pixelates, it's because of a weak signal. I doubt that it has anything to do with power quality. Sounds like the cable company is trying to find someone else to blame for their signal strength problem.

 

[Skogsgurra]

Agree fully with jghrist. There is nothing in a power cable that can influence a TV signal. You just tell them to do their work. Installing repeaters too difficult for them? Blaming mains voltage is a good old try - but has never worked in the long run.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[fredpar]

If that problem happening to all the cable customers associatted with the same transformer?

 

[dpc]

I have to disagree (a little). Overhead distribution circuits (say 5 kV to 25 kV), can be a potent source of RFI. Loose connections at insulators, bad terminations, bad insulators, etc can cause serious interference across a very wide frequency spectrum. (I agree that the "power quality" of the incoming AC power is very unlikely to be causing this problem.)

Having said that, it is also true that a well-designed and well-maintained cable TV system should be relatively immune to such interference due to the shielding provided by the coaxial cable (and probably the fiber backbone).

A good way to check for RFI from primary distribution system is with a cheap portable AM radio. If you have a noisy insulator or similar, it will be all over the AM band, and the directionality of the ferrite antenna in the AM radio can help you track it down.

 

[MrJam]

I installed a hioki 3196 on sight per-request of the cable company. I sure would like to have the answer for them, even if it’s not the power. Does anyone have any possible answer? The coax is shielded. I did notice the PVC conduit, that the main feed is pulled into the building in, is full of water. Could this effect the signal? Pixelation is only occurring on certain channels. The problem is occurring in an apartment complex. More than one unit is being affected and all the apartments are feed from one transformer. I know nothing about cable installations. Any ideas would be appreciated

 

[Skogsgurra]

"Conduit full of water" - I think that you have the problem there. Water does influence signal damping in a cable. Even if the water has not entered the cable.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jghrist]

I think you would be better off monitoring the cable signal instead of the ac power. You don't even know if there is an interference problem. It still sounds like a weak signal problem to me.

 

[l3city]

Maybe this comment is not what you are looking for, but change/repair that conduit, there is a big....big problem there, no water inside any conduit unless is used for pumbling.
On the other hand, there are several factors that might affect your tv (see above comments), cable length for example, sharing your signal with other tv's in your house or wherever you are, maybe all is needed is a "signal booster" to get a better image. There are new types of tv's like the High Definition TV which might have higher image requirement than just the cable coming into a huose, anyways, hope this helps

Regards, be happy

 

[dpc]

Your first post mentioned multiple houses being involved, but now it is an apartment building. Is this the same problem?

I have no idea what the cable company has already tried, if anything, but generally the first step is to determine if the problem is inside the building or outside. This can be done by connecting a TV directly to the cable just before it enters the building. If the signal has problems here, it is doubtful that it is a power quality issue. A small battery-powered TV could also help verify if problem is coming in on power lines. It could be RFI from another source using the power wiring as a means of getting in the the televisions. Cheap electronics are susceptible to RFI entering on the power lines. This is not a "power quality" issue because the RFI is not caused by the power system.

Who owns the cable wiring inside the apartment building? Crappy coax is a big source of problems, especially when installed by amateurs using the wrong tools and using cheap connecters.

A conduit that is "full of water" is a potential problem, although you can generally expect some moisture in an underground conduit.

 

[MrJam]

In my first post I mentioned multiple houses because that’s what I was told by the cable company. I'm sub contracting from the cable company. When I suggested monitoring for RFI, they informed me that they had the equipment to do that. They just wanted me to monitor the power. As a subcontractor I am only able to do what the customer, in this case the cable company, wants. I do not think the problem is being caused by the power. I downloaded the data from the monitor and found nothing significant just a few momentary voltage variations. I want to solve the problem, but I do not think they want to invest the time and money into it. So, I'll include many of your suggestions in the report. Thanks dpc.

 

[waross]

You may try disconnecting the cable and connecting your power monitor to the open end. This should show up any induced 60 hz. voltages. You may also try reconnecting the cable with jumpers and checking for 60 hz. circulating ground currents.
I doubt that the currents would affect TV frequencies, but the cable may have been degraded by excess heat caused by circulating ground currents.
I think that this is a long shot, but you may want to suggest it in the interests of a complete power check.
You would want the cable companies approval to interupt service in any case.
If you are allowed to disconnect both ends of the cable you can megger it to check for excess leakage to ground.
As I said, it's a long shot and the cable people probably have tests and equipment to check cable quality, but if you ask power people, you will get power people suggestions.
Let us know how it turns out if you are able to.
Good luck.
respectfully

 

[MrJam]

I recently spoke to an occupant of the apartment complex who is experiencing problems with his reception and he told me that the problem only occurs with digital cable.

 

[MrJam]

ADDENDUM:
Obviously the pixelation only occurs with a digital signal, but wouldn’t some interference be measurable on the other televisions in the apartment.

 

[DanDel]

MrJam, the only other thing you may want to check is the power system and cable system grounds.

 

[peebee]

I agree that the tiling & pixelating sounds like a problem more related to signal level than power level. That said.....

Regarding "There is nothing in a power cable that can influence a TV signal" -- note that TV pictures update at 59.9Hz, about the same frequency as the 60Hz power line. Power problems in general and grounding problems in particular can "beat" against the 60Hz power signal. On an analog set, grounding problems will often manifest themselves as a line or band which slowly scrolls vertically across the TV screen. I'm not sure what the result would be with a digital tuner.... but it would seem that any small signal disturbance could result in pixelation....

Note that proper grounding of the TV cable is also required by NEC, but despite the code and picture quality issues, grounding is overlooked and misunderstood by many cable TV installers. Although I'd really suspect the cable TV signal level rather than power or grounding, I second the recommendation to check grounding -- check for clean connections, bright shiny copper and water pipe, tight bonding clamps, etc.

I'd recommend also posting your question at avsforum.com -- there's a couple sharp video engineer types lurking over there, just make sure you have a good BS filter in place for those AV-philes more inclined to the mystical than the technical.....

 

[dpc]

On some cable systems, the digital channels are bunched at one end of the channel spectrum, meaning that they all may be operating at a different frequency than the analog signals.

Also, it's possible that the particular type of interference is more noticeable in digital mode than analog, althought that seems unusual.

Are the complaints clustered in a particular area of the building? Someone's computer could be putting out a lot of hash, coupled with a sub-optimal coax system. Is the problem intermittent at a particular time of day?

 

[MrJam]

The problem is intermittent. I had one of the residents keep a log. I don't have it in front of me, but from what I remember it appeared to happen sporadically through out the day at no set intervals. I believe it was worse late at night. I'm not sure about the clustering.

I inspected the area where the main cable feed enters the building and attaches to the block that feeds each apartment. I could not find a connection to the building ground rod. I know this is a code violation. Perhaps it could be the cause of the problem?

 

[itsmoked]

Sure could! Definitely!

I like the noise source angle too. Often someone will hook their cable into a nasty noisy computer that will conduct stuff back to the cable.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

The cable shield should be tied to the building grounding system as a safety measure, if nothing else. This is required by code, so I'd let the cable co. know about that. It may help the interference problem, but I wouldn't get my hopes up.