Coax Cable: quality difference?

[rsagetv99]

Originally Posted by Menehune

The commercial amps I have at work list the power leaving the output connector. I would assume the consumer models are the same-net gain.

I don't have a multi-output amplifier on hand to verify this.

OK, so if I am reading you right then if I have 10db coming in, then a two-way split for a cable modem would drop it to 7db, then if I plug that into an amplified splitter that reports 8db output then I will have 15db at each output?

I heard it mentioned somewhere (maybe this thread) that the cable company's goal is to get the signal to 0db at each TV. Is that my goal as well? If so then I would need to attenuate the signal if I am going directly into a tv from one of those outputs correct?

[stanger89]

Originally Posted by rsagetv99

OK, so if I am reading you right then if I have 10db coming in, then a two-way split for a cable modem would drop it to 7db,

Actually a ideal 2-way splitter would be a 3dB loss, but real-life ones are more like 3.5-4dB

then if I plug that into an amplified splitter that reports 8db output then I will have 15db at each output?

Basically, but it would be more like 14, 10 - 4 + 8. One more point though, each time you split you loose SNR, so when you go through that first two way splitter you'll loose 3dB of SNR. Now the amplifier amplifies everything, signal and noise, so it actually raises the noise floor. That's why you always want to amplify as early as you can, to maintain the lowest noise level possible. An amp right next to the TV won't do much good at all.

I heard it mentioned somewhere (maybe this thread) that the cable company's goal is to get the signal to 0db at each TV. Is that my goal as well? If so then I would need to attenuate the signal if I am going directly into a tv from one of those outputs correct?

I would only worry about attentuation if you're having problems.

[rsagetv99]

I'm getting some rolling horizontal ghost lines on some of my HD channels, that's why I asked about attenuating the signal. What is the idea signal strength at the end device 0db?

[stanger89]

You shouldn't get any ghost lines on an HD channel, unless they're in the bitstream. Either that or you've got a ground loop somewhere.

[rsagetv99]

I am connecting via component connections, could I be getting electrical interferance on that cable?

[stanger89]

Possibly. You're saying that you've got your cable box run component to your TV and get rolling bars on digital channels? Then you've almost certainly got a ground loop. A search will give you more/better advice on ground loops than I can.

[rsagetv99]

I think I'll try taking my Onkyo out of the loop, right now my component connections loops through the Onkyo reciever which acts as a switch-box. I'll try going direct.

But as a sidenote, what is the preferred db at the end device?

[stanger89]

I don't know, and since I can't afford the test equipment to find out what mine is , I don't really care.

That said, I would venture that if you've got +10 into the house, unless you've got say 2, 4-way splitters (-12dB or so splitter loss) I wouldn't bother with an amp.

[Menehune]

IIRC, the FCC mandates that customer equipment operate correctly with a minimum of -10dbm of signal at the jack, but the Cable Co engineers I've talked to design for a minimum of 0dbm. I've run signal inputs of +20dbm into VCRs without degredation. Above that, you can get excessive reflections in the TV tuner and picture degredation. Some of the cheaper off-brand TVs at work don't like more than 15dbm input power-picture ghosting and audio buzzing occur.

Shoot for 0db and remember that RG59 cable has 8db attenuation at 750MHz (approx channel 117) per 100 feet. RG6 has approx 6db attenuation at 750MHz per 100 feet.

[roofus]

Originally Posted by korben_dallas

Not sure if this helps any, but when the cable contractor came out to run a new jack, he looked at the setup I had for the TV & Sage PC and said I was using the wrong kind of splitter. He pulled one out of his truck and hooked it up. To be honest, I'm not sure I can tell a difference, but it was free so ok.

You were probably using a splitter under 1ghz, cable companies press that but you don't always get a better signal.

[roofus]

Originally Posted by rsagetv99

I'm getting some rolling horizontal ghost lines on some of my HD channels, that's why I asked about attenuating the signal. What is the idea signal strength at the end device 0db?

RF Isolator