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Removing Hum from Cable TV feed

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walter biscardi
Removing Hum from Cable TV feed
on Jan 6, 2007 at 8:06:04 pm

Hi guys,

What we have is our Panasonic 50" HD Plasma screen with two Component inputs. One input is from the Kona 3 via a Sony PVM20L5/1 and the other from our HDTV Cable box. When the cable box is connected to the plasma, we get a bad electrical hum in the picture, regardless of which input we're watching (Kona or Cable) and regardless of whether the cable box is turned on or off. It's a vertical rolling blue / red line that's faint, but very obvious in the darker images. The noise also affects the Sony. Completely disconnecting the Cable box from the plasma is the only way to get rid of the noise.

I know all about "hum-bucklers" but have never found one that really worked well. Any suggestions on how to address this issue? The part that perplexs me the most is that the noise is present even if the cable box is off.

Why do we have cable HD fed into our edit suites? Because we want to see HD programming on the exact same screens we're editing on to get a sense of what our stuff looks like compared to how HD broadcast looks. We watch a lot of Discovery HD Theater as a comparison.

Thanks guys for any suggestions!

Walter Biscardi, Jr.
http://www.biscardicreative.com
HD Editorial & Animation for Food Network's "Good Eats"
HD Editorial for "Assignment Earth"

"I reject your reality and substitute my own!" - Adam Savage, Mythbusters


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sacci
Re: Removing Hum from Cable TV feed
on Jan 6, 2007 at 8:11:20 pm

Have you tried a simple ground lifter?


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John Pale
Re: Removing Hum from Cable TV feed
on Jan 6, 2007 at 10:06:33 pm

I actually had a similar problem at home a few years ago...I called the cable company and they installed a filter between the cable box and the monitor that eliminated the problem. This was with SD, though.


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JeremyG
Re: Removing Hum from Cable TV feed
on Jan 7, 2007 at 1:06:24 am

I had the EXACT same problem. I got one of those power strips with the coaxial connection in it (effectively grounding the cable signal) and that cleaned it right up. I put that strip between the wall and the cable box. There was no way I was going to wait for the cable company to come and try and sort it out.

Jeremy


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Bob Zelin
Re: Removing Hum from Cable TV feed
on Jan 6, 2007 at 11:56:29 pm

BUT - if you are willing to call the cable company, and bitch at them, they will come and correct this. The problem is no different than 99% of the hum problems out there. They get their power for the RF distribution signal from a different power source (with a different ground potential), than the ground at your facility. 2 different grounds, means GROUND POTENTIAL, which means HUM. Let the cable company deal with this for you - its a common issue.

Bob Zelin


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JeremyG
Re: Removing Hum from Cable TV feed
on Jan 7, 2007 at 12:46:26 am

[Bob Zelin] "Let the cable company deal with this for you"

I guess I am so fed up with major utility providers that I have resorted to a do it myself attitude. I tried explaining a tech on the phone the I had hum bars, and even a grounding issue, and guess what...he was clueless. I even went so far as to follow the cable wire outside and see where it was grounded and REGROUNDED the damn thing.

A trip to MicroCenter and 15 dollars later, problem solved.

Jeremy



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Bob Zelin
Re: Removing Hum from Cable TV feed/hum
on Jan 7, 2007 at 3:13:55 pm

It is amazing to me that many "electricians" don't understand what a difference in ground potential is. Don't you have to pass a state exam to become an electrician? Don't you have to know what AC voltage is, to become an electrician. The simple concept that there is an AC voltage between 2 diffent grounds is a great mystery to many electricians - which drives me crazy - and of course, is the reason why there is hum in facilities - and owners scramble to say "gee, I must have a ground loop, or a bad ground wire on one of my audio cables - maybe I should start cutting off the grounds on these cables" - not realizing that their
electricicans are morons (and I ain't no electrician).

Bob Zelin


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walter biscardi
Re: Removing Hum from Cable TV feed/hum
on Jan 7, 2007 at 3:29:07 pm

Thanks for all the posts guys. I'll try the power strip with the RF feeds first as I think I have a few of those around.

Walter Biscardi, Jr.
http://www.biscardicreative.com
HD Editorial & Animation for Food Network's "Good Eats"
HD Editorial for "Assignment Earth"

"I reject your reality and substitute my own!" - Adam Savage, Mythbusters


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Tom Matthies
Re: Removing Hum from Cable TV feed/hum
on Jan 8, 2007 at 3:12:06 pm

We had a ground loop problem here a few years ago after some remodeling. All of the outlets in the "technical" area go hack to a common grounding point in the system. That's the meaning of those orange colored wall plugs. Anywoe, we had tarrible hum-bar problems after the remodeling. We called the electricians in three of four times to attempt to rectify the problem to no avail. I measured the difference in ground potentials for the electricians and pointed to it and said:"See, look at that. It's almost a two volt difference." The electrician looked at me with the same look that my dog gives me when I talk to him. Hearing but no comprehension. A couple of volts won't hurt you was the reply. I did my best to explain that the entire video signal we work with is about a volt. Two volts will completely ruin it. I wasn't concerned about the two volt difference actually hurting someone. Still, he didn't understand. Finally I tracked to problem down to the star grounding point that had been re-mounted using PLASTIC spacers. It was supposed to be grounded to a steel I-Beam but was instead basically floating the fround points of ALL of the technical equipment in that section. The hum problem occured when I tied that section into another group of graphics computers located one floor down. Ground loop central!
Anyhow, the plastic spacers were removed and all was well again. Plus we got charged for three visits by the electrical contractor even though they were basically useless and we found the problem ourselves. "Whatever" was the reply we received to that one.

Tom


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JeremyG
Re: Removing Hum from Cable TV feed/hum (MOVING OFFTOPIC)
on Jan 8, 2007 at 3:36:09 pm

Speaking of power problems, if you want to see a great documentary about power, watch Power Trip. Yikes.

http://movies.yahoo.com/movie/1808527128/info

Jeremy


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Bob Zelin
Re: Removing Hum from Cable TV feed/hum
on Jan 8, 2007 at 11:39:00 pm

TOM WRITES -

I measured the difference in ground potentials for the electricians and pointed to it and said:"See, look at that. It's almost a two volt difference." The electrician looked at me with the same look that my dog gives me when I talk to him. A couple of volts won't hurt you was the reply.


REPLY -
many people say "why is Bob Zelin nuts" - because I have to deal with this EXACT SITUATION you wrote about in real life on an almost daily basis, and if I become hysterical, these electricians will BEAT ME UP (so I take it out on you guys). The example you gave is often the EXACT SAME RESPONSE I often get - " a half a volt won't kill anyone" - and they look at you like you are an idiot. We all run so many wires, but for an electrician to run that extra white wire to the common "low" buss of the panel, and make sure all the grounds are in fact "grounded" back at the panel - well, this just KILLS THEM ! ("hey, my light bulb lights up").

Bob Zelin


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Wayne Carey
Re: Removing Hum from Cable TV feed/hum
on Jan 8, 2007 at 4:13:47 pm

Hey Walter,

I have to agree with all of the guys here and you do need to talk with the cable company about this. BUT when you are on the road, and you get this issue, APC (the makers of the power UPS) have a product for cable lines for the same issues. I'm not sure on pricing, but it may be something to look in to...

Everyone here is right... power is power but grounding is a science that can't be fudged in our industry. If the cable company places a hum filter and you still see it, call an electrician because you may have something going "south" in your building power. Circuit breakers do and will fail from time to time. I've seen this one many times myself. When I was working for a local PBS station doing a college basketball game, we ran into a serious surge that kept blowing the breakers in you production vehicle. The problem was due to a 220 breaker that lost its ground. A large enough hum will shut you down quickly.

Give it a shot!

_______________________________

Wayne Carey
Schazam Productions
http://www.schazamproductions.com


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