Re: [IRCA] Noisy cable TV

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

Keeping in mind all the information that has been offered, I re-inspected 
the situation and need to correct or confirm a couple of my earlier 
descriptions of the installation and situation, and report on other 
observations.

I verified there is no ground wire on the utility pole.  The telephone 
cable is the only line down the pole and then buried.

The cable drop connects through a grounding block which is grounded to the 
conduit running down from the main power fuse box.  The telephone ground is 
to that same box.  I had earlier described the cable ground incorrectly 
from my faulty recollection.  This is just as you describe, Rick, though 
there is no coiling of the cable and no gas-discharge device.

The conduit contains the only ground wire for the utilities, which exits 
the conduit just above ground level and then strangely runs along the base 
of the wall.  It gradually goes deeper but as far as I was willing to dig 
at it, there was no ground rod.  Houses in south Florida, such as mine, are 
often built on a concrete slab, rather than foundations you would find 
other places.  I suspect that the ground wire may be buried beneath the 
slab during construction, rather than use a ground rod.  Short of a lot of 
excavation, I have no idea where that ground wire eventually 
goes.  Possibly it was bonded to the rebar before the slab was poured -- 
this speculation is way beyond my realm of experience.

I had mentioned the cable grounding block was a splitter as well, but that 
was wrong.  The grounding block is that only, a short length of coax runs 
from there to a separate splitter.  The two cable coaxes go to only two 
things.  A distribution amplifier in the front of the house and a cable 
decoder in the back.  With both these disconnected -- effectively removing 
anything in the house from direct connection to the cable -- there was no 
change in the noise level on the cable coax.  This tells me the noise is 
coming into my house, not going out.  I hesitate disconnecting the cable 
drop at the grounding block because all of the connectors are sealed and 
I'd prefer not screw something else up.  For now I'm satisfied the noise is 
not my fault.

I have been monitoring the coincidence of DSL outage and detectable noise 
on the cable coax.  Cable was out all day yesterday and only came on late, 
when noise was found to be down.  Today there has been no significant noise 
and DSL has worked all day.  Until just as I type.  DSL went out, I first 
checked my receivers and noise was up.  Then I placed an AM radio near the 
cable coax and the noise was up.  As I was doing this at different 
locations the noise subsided somewhat and at the same time DSL 
returned.  The noise has been no where nearly as bad as previous days.  The 
DSL/noise pattern continues with further outages as I continue to compose 
this message.  Just now the raucous noise of yesterday began going on and 
off and finally settled in blotting out the frequency I've been monitoring 
(660kHz).

With just a weak Cuban on 660kHz (Radio Progreso, Santa Clara, VC) the 
noise level as measured by the relative 0-10 scale on my RX-320D, registers 
1 or 2.  It was below 1 earlier, before any of the cable noise began to 
pick up today.  That rises to 7 or 8 with higher peaks when the worst of 
the noise kicks in.  My antenna is 15 to 20 feet away from the over the 
roof cable coax.

A further observations is that this morning was overcast, the sun coming 
out around noon.  Now at 4:30 local, the sun is in and out of cloud cover 
and if heating is the problem somehow, the noise seems to be following that 
pattern.  The more sunshine the more noise.  That's one bad pattern in the 
subtropics.

At this point I am convinced my DSL problems are a direct result of the 
extreme noise.  Every indication is that noise comes from cable TV 
coax.  Also it seems that whatever the problem is, it is affected by 
daytime heating.

As both a good Floridian and someone with stuff that's broken, I'm hoping 
for a very sunny day tomorrow when the cable guy shows up.

Curt


At 08:39 AM 10/3/2006, you wrote:
>Comments in-line...
>
>W. Curt Deegan Wrote:
>
><Snipped here and there>
>
> > 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.
>
>That's good info. There usually isn't a ground on every pole.
>
> > 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.
>
>There are two distinctly different line levels associated with a CATV
>system. One is the longer distance trunk level, and this (after coming
>off of Fiber to RF) is not used to feed drops to users, but rather to
>feed trunk amps, which are daisy-chained together for a reasonable
>cascaded number. At any trunk amp signals can be split off and sent out
>at the higher level used for CATV distribution, and then on through
>directional couplers (taps and splitting devices) at poles, through line
>extenders, etc. fanning out and off to users.
>
> > 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.
>
>Also good info.
>
> > 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.
>
>It might be. Artifacts (that's what the CATV tech will call the blocky
>pixelation) is usually caused by an insufficient amount of data to
>reproduce the on screen picture. This can be caused by noisy data on the
>cable, interference on the satellite, or by low line levels feeding the
>digital CATV converter box in your home. Have your cable tech tell you
>the levels at several places in the television spectrum at your home. If
>the levels decrease to a point unable to be demodulated with enough data
>to display a full picture, you'll get artifacting. And, the levels might
>be changing, causing this. All levels on a cable system change a small
>amount with changing outdoor temperature, but not by great amounts.
>However, if your levels are just at the lower edge of usability, normal
>level changes during the day could cause intermittent and unreliable
>operation. A digital CATV signal pretty much either works or it doesn't.
>At the hairy edge, you'll see the artifacting before it locks up
>completely and stops decoding.
>
> > 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.
>
>That's fairly common. They put up a display that can be looked at using
>a signal level meter with a little LCD TV screen on it, or a small TV
>receiver. That way you can see what you are doing on the reverse path
>from the field.
>
> > 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 key to proper grounding and noise reduction is making sure that you
>have a single-point ground. This is almost universally at the power
>utility ground point. You'll have a heavy ground connected to your power
>panel and that should be the ground for the telco and the CATV also. The
>actual demarcs for the telco and the CATV should be near enough to the
>power ground to bond to that as their ground. What you don't want is a
>separate ground rod for any of the other utilities like the telco or the
>cable, or a connection to plumbing pipes. This is sure to cause ground
>loops and is really shoddy installation. Telcos are usually pretty good
>at doing grounding right and marking their tap to the power ground
>conductor with a nice warning tag to call them if it is loose or
>damaged, but some CATV installers are not so conscientious. I suspect
>that your local electrical code also requires this single-point ground,
>so you likely have plenty of leverage to make the installer fix it if it
>does not comply.
>
>Noise is still likely another issue, but the grounding can make a
>difference in radio noise. And, poor grounds can generate noise due to
>poor connections, etc. Disconnecting your cable drop at your home's
>ground block can tell you whether this is the case in short order.
>
>Generally you'll have what is called a ground block at the CATV demarc
>point. This is an F-81 double male connector with a ground screw and a
>mounting bracket. This will be tied into the power ground, then off from
>there to other splitters as appropriate for your devices. Sometimes
>they'll use the first splitter as the ground block. This is acceptable,
>but I prefer a separate ground block with a short coax jumper coiled
>several times in about a 3-inch diameter coil of 2 or 3 turns, and then
>on to the next splitter (nylon cable-tie it to hold the shape.) This
>acts as an RF choke to lightning surges and is a bit of added
>protection. A better and safer way to do the ground block is to use one
>of the Regal gas-discharge ground blocks. These look like a 2-way
>splitter with just the 2 output ports and no input. The case does the
>same job as a traditional ground block, but the device also has a gas
>discharge tube to shunt any surges on the center conductor of the
>coaxial cable to ground too. These are cheap, and really offer some
>added protection to your connected appliances. They work similar to a
>PolyPhaser on a radio antenna feed line. I've seen one of these Regal
>devices commit suicide and save the home electronics with no damage
>after the aerial CATV drop was vaporized due to a strike to the power
>pole at the rear of a home.
>
>Here's what they look like:
>
>http://tinyurl.com/mbdmy
>
>They also come in models with a built-in 2-way splitter, but as I
>mentioned, I prefer the coax coil as additional isolation on the shield,
>so don't recommend these.
>
>Here's the parent page of the above:
>
>http://tinyurl.com/zzb5r
>
>They're cheap protection compared to the price of a new television set
>these days.
>
> > 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.
>
>Again, disconnecting it at the house and taking a listen would be
>interesting. If the noise is still there, it isn't coming from the house.
>
>Good luck on getting this fixed.
>
>Rick Kunath


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