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In Reply to: Ground Breaker and digital cable. posted by DAVID on November 23, 2002 at 22:24:45:
I'm assuming that if you're listening to the hum and unhook the coax input to the cable box, the hum goes away?The device you are referring to does not really eliminate the ground, it just inserts a small transformer between the ground and the device at the end of the coax...in this case the digital cable box. A tranny shouldn't bother the digital box...everything should work ok. Transformers don't work with satellite systems [between the dish and receiver], however.
Such devices can solve problems, but if everything is properly hooked up, you probably won't need one. Let me elaborate...
The need for a grounding transformer is usually because the cable drop at the outside of the house is not grounded, or not properly grounded. You would be amazed and sickened at how many cable company "techs" have no idea how to properly ground your cable service. The hum you're hearing is likely due to a difference in potential of the two grounds [cable and electrical]. What you want is the cable service well grounded to the *same* ground point as the home's electrical service...that way all the grounds are equal.
The cable company should [and usually does] provide this service, free of charge, since it was their job to do it right in the first place. I'd call up their customer support and ask to have your ground redone. Then, make sure you're there when the service guy arrives so you can hold his hand. That all said, a coaxial grounding block and a bit of wire is cheap enough that you may wanna do this yourself to save the headache of dealing with the dunces at the local cable company.
:-)
Steve
Follow Ups:
Well, I couldn't resist joining in on this topic. First off, I am a CATV technician. I have been to numerous schools and deal with EVERY part of the RF/Fiber plant of the CATV system. Don't assume all CATV installers or techs are "dunces". 90% of all noise problems are generated by the customers VCR, TV, or bad jumper wires (most with push on ends) I have NEVER seen noise caused by an improper or non existing ground. The primary reason for grounding the cable at the point that it enters the house is for electrical protection. Proper grounding is grounding the splitter or protetctor within 20 feet or less of the POWER ground. The differnce in the two grounds can be a problem, NOT with noise. The problem comes into play when the cable has a good ground and the house has a poor ground or no ground. If the house were to loose the neutral connection with the power line, it will use the cable drop as the house ground. This can be very dangerous. This is why we ground to the house power ground. There is 15 dbmv differnce between the audio carrier and the video carrier in an analog channel within the 6 mhz of bandwith that it takes up. The digital is converted from digital to analog via the convertor box and the same is true whith its levels. This is why bad connectors and jumper wires are the culpruts of many a audio problem. Voltage on the line typically shows up on the tv screen as rolling horizontal lines or "hum bars" These usually start at the bottom and work their way up the screen. Usually there will be 2 bars on the screen at any given time, this is due to the fact that power is 60hz, and the tv scans each half at 30hz and then combines them.
nt
I saw the (RF) at the end of the title of your message and somehow made that read (NT) in my head. So, I didn't actually read your post, unitl just now.:-)
Steve
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