What do these numbers on a cable splitter really mean?

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Hello all,
I have been having problems with my cable modem. I split the line where it comes in the house. One leg to my modem, the other to the TV.
My internet kept dropping signal. I was sure to get a splitter that provided a direct pass-thru to 7dB on both outputs.
There is a three way splitter on the line coming in from you pole. It has output 7dB, 7dB, and 3.5dB.
Anyway, the cable guy came out and switched the hookup on the three-way splitter. He took the line that goes to my cable modem and TV off of a 7dB terminal and out it on the 3.5dB terminal. All is well now.
how is this possible?
Thank fred.
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Hello all,
I have been having problems with my cable modem. I split the line where it comes in the house. One leg to my modem, the other to the TV.
My internet kept dropping signal. I was sure to get a splitter that provided a direct pass-thru to 7dB on both outputs.
There is a three way splitter on the line coming in from you pole. It has output 7dB, 7dB, and 3.5dB.
Anyway, the cable guy came out and switched the hookup on the three-way splitter. He took the line that goes to my cable modem and TV off of a 7dB terminal and out it on the 3.5dB terminal. All is well now.
how is this possible?
Thank fred.
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The 'db's are attenuation. The signal from the 3.5 db output is TWICE as big as from a 7 db output. He merely doubled the signal to your cable modem, which is reasonable. If you still have good pictures on your tvs, all is cool and good.
Lee h

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The numbers on the splitter tell how much signal loss there is in the splitter. To split a signal 2 ways requires atleast a 3 db loss. From that you can split it more and each time you will get more loss. Internally your splitter seems to split the signal to two parts and one goes to the 3db port. The other goes to another internal splittter and that split gives you the 7 db loss for each output. It is a log scale so that means a 3 db will loose half the power, 6 db will loose 75% of the power, 7 db will loose about 80 % of the power, 10 db will loose 90% . The db loss numbers add so that 3 +3 = 6. There will usually be some fractions left over in the losses so that is why you get 3.5 and 7 for the losses. Cable modems usually need more signal to work than the tv sets. My cable comes to a 2 way splitter. One goes directly to the cable modem and the other goes to another splitter that goes to the other tv sets in the house. The modem works fine and the TV sets (one with digital box, two with the basics) have good vidio on them.
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You have to be sure it is a 1ghz splitter and not a 900 mhz for the internet portion of it. Digital TV does better through the gigahertz splitter also. They're kind of hard to find except through the cable co. But not impossible. Try radio shack.
--
Steve Barker


"Fred Wilson" < snipped-for-privacy@comcast.net> wrote in message
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Steve Barker LT wrote:

900MHz vs. 1000NHz(1 GHz, so that ~10% difference makes visible difference. You must be a fan of those super expensive Monster cables.
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Actually not. Won't even look at them. But my RR modem will not work through a 900 Mhz splitter and works flawlessly with the 1Ghz splitter that is on it now. And yes, it makes a visible difference. Otherwise there wouldn't be such an animal.
Screw monster cables. They're for yuppies kids.
--
Steve Barker



"Tony Hwang" < snipped-for-privacy@shaw.ca> wrote in message
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Lowes has a good selection too. That's where I got my last digital spliter when I was upgrading my dad's cable system.

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On Sun, 09 Jul 2006 22:56:58 GMT, "Steve Barker LT"

Higher frequency splitters are easier to find now that they are used for satellite.
--
Mark Lloyd
http://notstupid.laughingsquid.com
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On Sun, 09 Jul 2006 22:56:58 GMT, "Steve Barker LT"

My cable modem is a Motorola SB5120, which can provide information about the connection. According to its status page, the downstream (receive) channel is on 117MHz (channel 99) and the upstream channel is on 35MHz (T-12?, below channel 2).
--
Mark Lloyd
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Fred Wilson wrote:

For one thing, the signal coming from the 3.5dB port is 3.5dB stronger than that from the 7dB port, the numbers in question being the level of attenuation relative to the input port. That increase in signal level might have been just what was needed to improve the situation. Of course it might have been just a bad connection and any disconnect-reconnect might have fixed it just as well.
--
John McGaw
[Knoxville, TN, USA]
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Fred Wilson wrote:

That splitter must have some attenuator(simple resistor netowork or such) built-in. Any splitter, connector introduces certain amount of signal loss. When source signal is marginal this can become an issue.
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Follow-up if I may...
So is it possible to drive the signal too much?
Where might I find the best splitter to up in there? I have the modem off one leg and a digital tv off the other. Can I get a splitter that directly passes through the signal on both output legs with no signal loss?
Thanks.
Fred
Fred Wilson wrote:

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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).

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Mark Lloyd
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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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