What do these numbers on a cable splitter really mean?



Normally you can not have too much signal comming from the main cable. You can not get a splitter with out any loss. Think of the signal as money in the bank. YOu only have so much to start with. It is up to you to decide on what to do with it. If you spend a lot on food, it leaves less for say playing golf. You decide if you want stake or hambuger and a good set of clubs or a less expensive set. You can get a booster or amplifier for the signals to the TV sets if they are not clear.
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The TV both analog and digital is clear BUT on the digital channels the sound skips sometimes and does not match up to the picture.
Ralph Mowery wrote:

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On Sun, 09 Jul 2006 17:44:18 -0400, Fred Wilson

All you have to do is unscrew the cables, and interchange them.
Sorry, couldn't resist.
I can't really answer your question I think, except to say that those numbers do not represent output levels. For one thing, since no one knows what the input level will be. And splitters are passive, so output depends on input. So 7db is not more than 3.5.
Rather, when not referring to sound itself, I think decibels are a ratio, and 3.5 decibels represents how much signal loss there is going through this splitter. So 7db would be more loss than 3.5, not more signal.
I don't have cable internet, but I had cable tv and still have lots of tv's running off the output of my vcrs. For every three splitters I put into the system, I would have to put in one signal amplifier (or amp/splitter combination).
I have 6 tv's that will show the same thing, whatever comes out of the vcrs or the master antenna. And to do that I had to put in 2 signal amplifiers. How they will work with cable internet, if I ever get it, I don't know.

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wrote:

The numbers are pure ratios. They are really loss ratios so the lower the number the less loss. Whatever the input signal is , the output will be that many db lower. As I mentioned above the ratio is a log function and while 3 db is twice or half as much (the spliters may not show the negative sign to indicate loss), 6 db is 4 times or 1/4 as much depending on gain or loss.
If you get cable internet, usually a splitter is put in so that the modem is fed with a 3 db loss port. Then if you want more than one computer , you get a router and run cat 5 cable to each computer or use a wireless router.
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wrote:

Decibels do indicate ratios. 3db loss means 2:1 power ratio. Since perfection doesn't exist, the loss through a normal 2-way splitter will be greater than that.

Note that the need for amplification depends on the actual signal levels, no simple rule will always apply. If needed, an amplifier should be located BEFORE the cause of signal loss.

I have a similar setup. I can tune any of my TVs to channel 70, to watch whatever is playing on my main A/V system (although this doesn't yet include HD). This is switched between cable, satellite, DVD, and computer A/V.
In my setup, the incoming cable first goes to a 2-way splitter, with one output dedicated to a cable modem (digital cable would require the same setup), then it's combined with the output of my channel 70+ modulators (for local distribution), then to a distribution amplifier (really an amp and a splitter in the same package) and the necessary splitters to reach every TV in the house (as well as recording devices: VCR, PVR, etc.). Only one amplifier is needed even though I'm distributing signal to 10 devices (6 TVs, VCR, 2 PVRs, computer video digitizer).

A cable modem is a 2-way device, and so cannot be used across an amplifier unless that amplifier is designed to work both ways. The upstream channel normally uses a frequency lower than any normal TV channel (<54MHz).

--
Mark Lloyd
http://notstupid.laughingsquid.com
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wrote:

OK. Maybe I'll get DSL instead, or just reside in dial-up land until I get a raise.
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wrote:

Maybe you don't need an amplifier for a cable modem, if you split the signal to IT first. That's what I have here.
--
Mark Lloyd
http://notstupid.laughingsquid.com
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replying to mm, im2late wrote: Actually that is incorrect. The ratings of -7dv, -7db and -3.5 db refer to the signal LOSS when the signal passes through those outputs. A two way splitter will lose 3.5 db on each output, but on some three way splitters, one output loses 3.5 and the other 3.5 loss is doubled on the 2nd and 3rd output (i.e.-7db signal loss per output.) I would suggest connecting your most "demanding" or important device to the -3.5 output on the splitter for less signal loss.
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