Skkitzzo

So I've used em time to time in remodels when they dont wanna call the cable company out to do it, but ive always wondered what the difference in Db is between the two or three connections that have the same Db rating, and then theres always one with a little lower of a Db rating. Just wondering what those ratings meant, or if they're even ratings to begin with

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chenley

"Loss (approx) on splitters, 2 way = 4db, 4 way = 8dB, 6 way = 10dB, 8 way = 12dB"

Got this from: http://www.aerialsandtv.com/ampsandsplitters.html

Quite a bit of information on that site.

Greg

It all helps keep the signal balanced so you don't drop everything at the first point of attachment. Think of it as a voltage divider. Every TV has a specific impedance and they are not all the same. This insures each TV get an equal amount of signal.

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hbiss

Quite a bit of information on that site.

Unfortunately that's a UK or European site. The equipment and what they talk about hasn't much to do with what we have here in the US.

As to the original question- those db numbers on splitters tell you how much signal you lose when you split one line into two, four or more lines. The general rule is you always lose 3.5db every time you split a cable in two. That's why a 2-way splitter will be marked with -3.5 at each output.

Larger splitters are really just a bunch of 2-way splitters combined within the same housing. If you connected three 2-way splitters together with the two outputs on the first feeding the inputs of the second two you will have four outputs. If you follow each signal path from the input of the first splitter to one of the four outputs and add the 3.5db loss through the first splitter to the 3.5db loss of the second splitter you have a loss of 7db. That's why it says -7db on the outputs of a 4-way splitter.

Now can you figure out why most 3-way splitters have two outputs with a loss of 7db and one with a loss of only 3.5db? Hint- think about two 2-way splitters.

Splitters can be had with as many as 12 outputs or more. Smaller ones can be combined to do the same thing. Larger splitters tend to get a bit more efficient and can have less than the -3.5db per 2 way split.

So, what does this db loss stuff mean? It tells you that each time you split a cable you lose something. Do it often enough and you won't have enough.

How do you use these numbers and how do you make sure that you provide enough signal to each jack? First you have to know what you are supplied with then you use simple subtraction. If you don't have signal level measuring equipment a very loose rule is that the cable company will supply you with a signal level of +10db on your drop. You want to supply your jacks with a level of no less than 0db. So if you split the drop four ways the loss would be -7db through the 4-way splitter and you would end up with +3db at the jacks, not counting the loss from the cable itself. This is perfect.

I should note here that when you run your cable, each run from a jack should be home run back to the splitter location. Daisy chaining is not allowed.

You can see from this example how you can get into trouble when you need a large number of splits. You can quickly go below that 0db spec for the jacks. In cases like this there are amplifiers available. Amplifiers should always be located ahead of your splits and supplied directly from the cable drop. The amplifier should be chosen with the proper amount of gain (also rated in db) to make up for the combined splitting loss. It can also compensate for a low signal level on the cable drop if you can determine what it is.

There are several types of amplifiers out there. One type is available with a splitter built in and will have several outputs. These provide just enough gain to offset the built in splitter so the net is zero loss. Other amplifiers have a single output that is used to supply your splitters. Some are a fixed gain, some are adjustable. There are big amplifiers available too and you can get in trouble with too much signal. The rule is no more than +10db at a jack, so unless you know what you are doing and have the equipment and knowledge to measure signal levels don't be tempted to go the "bigger is better" route.

What I described here should give you a basic understanding of how to design a simple residental CATV distribution system. There is actually much more to understand if you want to make a profession out of it. But this should put you in the ball park so that you can at least give your customer something that is done properly.

-Hal

JohnJ0906

Is there a meter that you recommend for this?

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hbiss

I haven't used it but the Sadelco Display Max 2000 looks to be a good choice without spending thousands of dollars.

http://www.sadelco.com/dmaxjrspec.htm

-Hal

cdnelectrician

Check E-bay, I bought mine on there for about 160 dollars. Watch what kind of connectors you use too, cheap splitters and connectors wreak havoc on HDTV and cable modems. I only use the thomas and betts snap and seals, belden quad shield cable and antronix splitters when I do an install.

http://www.ptltest.com/WindowLiteInstaller.htm

GregS

I'm the same except for the quad shield.. No real reason for QS unless it's wickedly noisy isn't there?

cdnelectrician

This is true...when I did do resi most of the homeowners I did work for (high end custom houses on the lake in Bronte or Oakville) actually requested it. My old boss bought quite a few boxes of quad because he got a deal on it at white radio. To be honest...if I am wiring a house for the difference in cost between single and quad...why not use quad. It is a B&^%h to terminate though... Never had a problem selling the customer on the idea. It's standard with a lot of A/V contractors now. And I hope to never be on a resi job ever again unless it's my house!

electricguy

I exclusivly use gilbert ultra range RG 6 connectors now... they work on quad shield and conventional RG 6

GregS

Due to a pricing glitch at a supplier yesterday, I managed to pick up 2 spools of RG6 QS for $98 each. Now I gotta order some more TnB SnS for RG6 QS PDQ!

I&CMAN

where do you recommend I get the jacks/splitters for cable installation. I am moving into new house where cable(cogeco) is pre-wired and cable installer wants something like $30/jack....its a simple termination and and a plate...wire is already run. I have HDTV and dont want to degrade signal if I couple a wire or split. I noticed you mentioned oakville , that's my location. I am not sure which supplier in my area carry these items?

carolinasoutdoor

You definetely want to get compression style connectors. Screw on connectors are going to cause you problems.

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