Splits and Amps and Modems

David Lindsey

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Dec 22, 2006
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David Lindsey
I thought COX was going to handle this but the tech they sent out was gonna daisy chain 4 splitters in order to get me 8 signals. Ummm.....NO! FYI the service I have is digital and TV/Internet come in on one Coax cable.

I did all the multimedia wiring in the house. One outside line comes into the house. I have 7 locations for CATV and I also need to hook up one modem then get the modem to an ethernet router.

My question involves splitting the signal. One 8-way splitter would work physically, but I don't know what is going to happen to the signal. Do I need to put an amplifier in the mix? What happens to the internet leg of the splitter? Does it matter? What is the best way to do this?

Should I put the amplifier(what size) before the splitter? Should I get 2 1 into 4 signal amp/splitter combos?

Recommendations on hardware and where to get it would be nice as well.
 

Jason Adams

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Roger Jason Adams
Yeah...I need to know the same type of info. Currently in my house theres two splitters for the 2 cable boxes and the cable modem, and a few channels just wont show at all! Anything I need to do?
 

David Norman

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Best site for overall information on amps and splitters:

http://www.cabletvamps.com/education...Cable% 20Amp?

Actually the http://www.cabletvamps.com/index.htm site itself is a wealth of information about CATV, splitters, amps, etc.

Overall I would be suspicious about the mutiple splitters unless the guy is measuring signal levels at each endpoint otherwise it's likely that some TV's could be getting 8-16X the signal at the beginning splitter vs the TV at the end of the chain since each split is going to give you 3-4 dB signal loss (3 dB generally figured as a 50% signal decrease). It's possible they are taps instead of standard splitters which could work giving each TV essentially the same signal level. With cable boxes and cable modem/internet there has to be a return path so you can have 2 way information.

If you have a distribution point inside the house where the single cable comes in to meet all your wiring to the individual TV's and depending on the incoming signal strength, I would suggest trying either an Electroline EDA-FT08100 or possibly EDA-UG2802. The latter may not work with the modem unless split that line off first with a birectional 2 way splitter sending one line to the modem directly and other leg to the 2802. Electroline seems to be considered a Pro Line model and is often used by the Cable Co. themselves.

The guy who runs that site has a pretty solid reputation and sells through his website and on Ebay though you possibly could get the pieces cheaper elsewhere. Many here and avsforum have bought stuff from him.



This really depends on the strength and quality of the initial cable line in. If you have a really strong signal you may not want to amplify it more, if it's already borderline or even average, by the time you split it 8 times (11.5-12 dB loss -- about 5% your beginning level), you'll likely have all sorts of problems particularly with the Cable Modem. Unfortunately it's almost impossible to measure the strength/quality on your incoming line without the Cable guys meter unless you have access to some pretty fancy electronic. I've looked for years for a basic signal meter without much success -- the cheapest I've ever run across was well over $100. Some folks have a buddy who works or has worked CATV install and they have meters that you might borrow.
 

David Lindsey

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Dec 22, 2006
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David Lindsey
So assuming that the incoming signal is where it needs to be from the cable company:

The main line when split with a 2-way will lose 3.5dB to each leg. Internet will receive one of those. The other will then hit an 8-way splitter which will lose 11dB. So if I amplify the signal going to the 8-way with a 15dB amp then it will be very close to the incoming signal strength at each leg.

3.5+11=14.5 dB loss

15dB gain will neutralize the loss.


Then, if I measure the signal after the 8-way, what is the ideal number to have coming off of each leg of the split? For example, if I have a strong inccoming signal and after the 2-way I am getting +20dB, the 8-way will reduce that to +9dB. Is that a good place to be? What is the range of good signal numbers?
 

David Norman

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Sounds pretty close to the idea. Again measuring the actual incoming voltage seems to be the kicker.

The best information I have says the individual TV's strength should be somewhere between 0 and +10 dBmV though you may get a decent signals from -10 to +15. Too little signal and it gets ugly, too much and it may overdrive the Tuner.

In addition to the splitter loss, there is cable loss with RG-6 cable of around 1.5dB/100ft for low frequency channels (Channel 2 CATV) and 4.8dB/100ft for high frequency (Channel 78 CATV). It gets real complicated when you start getting into frequency/tilt slopes because low frequency and high freq. signal are treated differently. You probably would prefer to have a max differential between the highest and lowest frequencies of around 10dBmV within the above guidelines.

Bottom line is what the picture looks like at the TV with some sets being a bit more forgiving than others.
 

David Lindsey

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Dec 22, 2006
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David Lindsey
Does the run length come into play after the amp? If that is the case, my longest runs are no more than 40-50 ft which should not pose a problem.
 

David Norman

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If you know the strength at any point in the run, then only the length of cable after the measurement point is important. Overall it's probably a pretty minimal point in most homes though I guess if your cable is routed through multiple floors or in a roundabout way it might make a difference. At less than 100 feet, I'd suspect it's pretty much a non issue especially if all the cables are about the same. It becomes more of an issue when you have several 10-20 foot runs and a couple 100+ foot runs, then you have to get a bit fancier with how you do the amplification.
 

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