Re: [IRCA] Noisy cable TV

["W. Curt Deegan" <WWWR@xxxxxxxxxxxxx>]

Rick,

More good info it will take me a while to go through.  I can only answer 
some of your questions.

There is no ground on the new utility pole that I noticed.  I'll look again 
tomorrow.  The noise can be nulled and points to the pole -- and to the 
cable coax from the pole -- but it's not possible to be more specific.  The 
noise does not appear on power lines or phone lines in the house, just the 
cable coax.

There is no such thing as cool weather, there is hot, and not so 
hot...south Florida, don't you know. ;-)

It's tough to compare the pole installation to others because this pole has 
a junction of a major -- 2+ inch thick -- TV cable, splitting and going off 
in two different directions.  There is a large black block hanging on the 
cable with two less thick cables and smaller leads coming out, I assume 
this is a junction for the local drops and the split.  The only pole 
mounted box is telephone.  There is no power transformer, the local drops 
tap directly into the three power wires on the pole.  All of the power line 
fixtures are new along with the pole.  The phone drop was replaced and 
buried several months ago.

Now that you mention it, there are occasions especially during the day, 
when digital TV signals lock-up or pixelate for several seconds, I've not 
thought to relate that bad behavior to the other problems.  I assumed this 
to be satellite signal reception problems at the cable company.  Otherwise 
the TV quality is as good as it ever has been.  The system has undergone 
recent upgrades -- that was the excuse for extended outages, a least -- but 
does belong to Adelphia Cable which is bankrupt amongst other problems, and 
being divied up between a couple larger scavengers, so who knows what's 
going on.

No so long ago, tuning to unused channel 117 brought up a camera focused on 
an oscilloscope face.  No doubt related to system performance but I have no 
idea what the trace represented.  Unfortunately, when I check now my TV 
screen goes black, indicating something is there not just noise, but not 
the nifty scope display.

Grounding by the various services at the back of my house is best described 
as inspired.  The house is nearly fifty years old and some of this stuff 
has been there since day one, some of it is just a few months old, and the 
rest lies somewhere in between.  There are the three utilities as well as 
junction boxes for the pool pump fuses and the timer.  The cable TV 
grounding block is actually connected to a conduit descending down from the 
pool pump fuse box and seems to contain a ground wire, but is not itself 
part of the ground.  This immediately caught my eye, but will need closer 
examination to decide just what is grounded to what.

The most telling clue I think, is the strong noise that can be heard 
placing an AM radio (I don't have a VHF radio to try, plus I have digital 
service which I assume would act differently than analog) next to the Cable 
TV coax at the front of the house, completely away from all the other 
services at the back.  The noise is raucous there and can be tracked back 
through the house right under where the cable coax crosses from front to 
back along the roof.

Afraid I'm providing a whole bunch of disjointed information, but the 
comments from the list have been great.  I am going to keep all the good 
suggestion in mind and hope the cable guy can use some of them to track 
down the problem.

Thanks.

Curt


At 08:33 PM 10/2/2006, you wrote:
>Here are a few thoughts...
>
> > The idea of disconnecting at the pole to see if cable is what's causing 
> the
> > DSL problems is a good one.  Move the probable noise source as far away as
> > possible.
>
>I'd disconnect the CATV drop at your demarc and see if the noise changes
>first. You can do that yourself. Do an inspection of the grounding
>scheme for the three utilities, power, telco, and cable, and describe
>for us what you have.
>
> > I walked my portable radio along under my cable drop out to the
> > distribution pole in the back yard, and the noise followed me all the
> > way.
>
>Can you null the noise using the ferrite loopstick in the radio, and
>does that null point to an area on the pole? A bad electrical insulator
>maybe? Unattached ground on the pole, unattached ground on the CATV
>hardline? Is there a CATV ground at this particular pole?
>
>The noise couldn't be caused by an imbalance in the telco drop causing
>it to radiate could it? If you had one side of the DSL drop opening, or
>a bad DSL filter, you might unbalance the DSL drop and cause it to fail,
>generating the noise as a byproduct. Your DSL drop is a balanced
>feedline. (That's how it rejects common-mode noise.)
>
>If you have CATV egress you'll be able to hear video carriers leaking
>out of the cable, and a good spot to listen is in the 145.25 MHz area,
>but you can find a CATV frequency chart and look for any of the TV
>carriers with a VHF radio or scanner. If you have egress, you'll hear it
>for sure doing this.
>
> > Not definitive since the power lines go that way too, and the phone
> > lines are buried along the same path, but still.  While there are power 
> and
> > telephone lines on the pole, there is a junction of a major cable line 
> from
> > the south that splits in two directions east and west for local feeds, 
> from
> > that pole.  Walking across my back yard east under the three utility
> > services' overhead lines, the noise dropped off as I moved away from the
> > pole.  Tomorrow I may try walking along the perpendicular cable line to 
> the
> > south as well as the westward feeder, just to see what happens to the
> > noise.  With my luck it is all fed directly into my house!
>
>Is there a CATV node or line amp on this pole? These will have AC power
>fed forward to them from a CATV power supply located on a pole some
>distance away, maybe a long way away. If there is a CATV connector
>suckout you may have arcing going on, though if this is the case, you
>should be able to see it on your television signals. Do you? You might
>have cracked hardline, loose hardline connectors, a defective
>directional coupler at the pole, etc.
>
>What you are describing though, sounds like it could be conducted power
>line noise. Any ideas there?
>
> > It is interesting to note that the occasions of extreme noise began around
> > the time that very utility pole was replaced and all the services moved to
> > the new one.  Possibly that procedure damaged something and created the
> > noisy situation in so doing.  I had always been suspicious of that but had
> > not traced the noise to the extent I have the last couple days, since it
> > has gotten far worse.
>
>Have the CATV line tech inspect the pole carefully while he is on scene.
>Wiggling the hardline and the various connections, etc. Also have him
>listen for arcing above his head in the area of the power line while he
>is up the pole.
>
> >
> > Your comments on sunshine and day/night problems is also very
> > interesting.  During a recent period of cloudy rainy days, my DSL was
> > pretty good, though lightning in the area would disconnect it.  The last
> > few days, during which I've had no daytime service, the days have been
> > bright and sunny.  I had been hoping once the thunderstorms subsided, my
> > DSL would stop frequently going out.  Instead, as the nice weather moved
> > in, I lost DSL entirely, during the day.  Now that you mention the notion
> > of daytime heating aggravating the problem, the correlation becomes 
> evident.
>
>Unless you have an egress issue with the CATV plant, nothing failing
>CATV node or amp wise should be able to escape the CATV plant and affect
>you. The cable plant does self adjust itself with temperature changes,
>and a mis-behaving ASC or AGC circuit in a CATV active device can cause
>various issues, but you'd see these on the video for sure. Are you?
>
>Suckouts due to bad connectors are worse with cool weather as the
>aluminum hardline changes dimension quite a bit with temperature
>changes. Again, is the sufficient strain relief at the new pole? Look at
>other poles for an idea about what the installation should look like.
>
> > I'll keep these ideas in mind and hope the cable guy is willing to listen
> > to suggestions.
>
>Let's hope you get a line tech and not an installer, who won't have the
>necessary equipment or experience to really handle the issue. If you do
>get an installer, insist that they send out a line tech to finish the
>job if necessary.
>
><Snip>
>
> >> At 03:57 PM 10/2/2006, you wrote:
> >> It almost sounds like the cable feed is leaky somewhere and emitting
> >> extraneous noise that is most likely either their Internet feed or control
> >> signals (for addressable cable boxes, pay-per-view,etc).  Both of those
> >> operate on very low frequencies that often include MW and LW on many CATV
> >> systems.  Or it could be a bad repeater/amplifier on the cable trunk 
> in your
> >> neighborhood.
>
>If there is leakage, you should be able to detect it using the ideas
>described back up the page a ways. Since the VHF leakage will travel a
>lot less distance wise, you should be able to narrow down the area with
>the egress problem a lot easier using VHF. Who knows, it may be a self
>install of something by a neighbor or something on the CATV aerial
>plant. If you have MW leaking out you'll have other stuff leaking too.
>
> >> If it's strong enough to disturb your DSL, that's pretty bad.  I would
> >> recommend that the CATV Technician disconnect the cable feed at the 
> pole and
> >> see if the noise goes away.  Then check your DSL to see if it's 
> working.  If
> >> everything seems normal, have him reconnect the cable and see if the 
> problem
> >> returns.  If it does, you will have then proven that the interference is a
> >> Cable TV problem.
>
>Maybe, but it could be more complex. DSL does use RF frequencies, and
>CATV return path leakage just might be able to affect this, again, look
>for telltale egress signs. If you can find the leakage evidence, you can
>find the problem, and the cable tech will have to fix it right then and
>there if the leakage is bad enough, that or shut off the entire area.
>
> >> My guess is a noisy amp in the neighborhood whose signal level is so 
> strong
> >> that it blasts through the cable.
>
>Probably not the cause, even with a misbehaving amp, there still should
>be  no egress, and no effect to anything outside the cable plant.
>Besides, if this was the case, you'd have seen them there fixing the amp
>already as there would be video (likely) and cable modem complaints from
>users. But who knows...
>
> >>Why it would only happen during the day
> >> is anybody's guess.  Given that you're in Florida, it could be that
> >> something in the CATV system nearby is heating up during the day and 
> causes
> >> the noise.
>
>CATV plant losses decrease with lower temperatures. As temps increase
>active devices that measure the ambient air temperature increase the
>amplifier gain and the slope (higher frequency pre-emphasis) to
>compensate. Hardline also changes dimension with heat and cold. This can
>get interesting when compensation circuits get out of whack, but I
>guarantee you'll have visual evidence of this on your television or
>evidence of dropouts big time on the reverse path if this is happening.
>
>You have got a lot of good ideas from folks and hopefully some of these
>will lead you to the problem.
>
>Rick Kunath


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