Cable splitting question...

[1tribeca]

I just purchased a 4-way splitter at HD. When I went to replace the exisiting 3-way the cablr folks installed, I noticed one of the outputs (the one feeding the modem) was 3Db...all the rest were 7Db. The splitter I grabbed has all 4 at 7Db...I didn't hook it up in case I fryed something!!! Is this a necessary difference and if so, why?

 

[markw]

You'll be fine. It's just an indication of signal strengeth to each leg.

Splitters are passive devices. You can't burn anything up when there's no power being input.

Your signal has only so much power. By splitting it you share that power between each split.

When you split a cable signal in two, each leg is a little less than half the power of the original signal, or 3 db down and figure another .5 db for insertion loss.

If you then split one of those two legs (each of which is already 3.5 db down from the original signal), that means each leg is about 7 db down from the input signal.

Depending on your signal strength, you can rally only get so man y splits before your picture starts to suffer but if you had three before, odds are pretty good that four will still probably work.

 

[AverageJoe]

Most splitters are the electrical equivalent of a series of two-way splits with each leg losing 3.5 dBmV of signal (sometimes rounded up or down to 3 or 4 dB on the label). The 3-way they used was basically a 2-way with another 2-way on one of the legs, so you had 7 dB loss on two legs and 3.5 on one (they do make "balanced" 3-ways with 5.5 dB loss per leg, however).

With the additional port on a 4-way splitter (the same as another 2-way on the 3.5 leg above), you have equal 7 dB loss on all legs. If you bought an 8-way splitter, you would in effect be adding a 2-way in front of two 4-way splits giving you about 11 dB of loss per port.

All that said, you should be fine installing the 4-way in place of the 3-way. The only port that changes is the one feeding the modem, and in most cases the additional 3.5 dB signal loss won't hurt you.

 

[AverageJoe]

Mark beat me to it (I type slow). Good job.

 

[markw]

Mark beat me to it (I type slow). Good job.

Thanks. Back at ya. I'm just glad we both said the same thing.

 

[1tribeca]

You guys are bang on! I hooked up the 4-way...seems to be fine. I was also gonna sink the cable into a shallow electrical box in my kitchen wall (has to shallow...2" stud on block wall) but the guy at the hardware store alerted me to a thin connecting plate that won't cause any interference etc. to the signal...cool find.