Splitting TV cable service

February 26, 2007 5:46 AM

I have TV cable service to my house. I would like to split it six or seven ways to allow cable access from rooms throughout the house. I would never use more than three of the lines at a time. Will this work or will the signal be diluted somehow?
posted by retiree to technology (13 comments total)

It should work but typically you need cable boxes for each location.
posted by JJ86 at 5:50 AM on February 26, 2007

As JJ86 alluded to, you may need cable boxes for each TV. I get basic cable though (not digital), which doesn't require a box, and so I've got the wire running to about 8 outlets in my house. I don't think the number of times you split it will affect the signal, but the length of cable you run might affect it, in which case you'd just need to buy a $20 signal booster.
posted by Doofus Magoo at 6:03 AM on February 26, 2007

Be careful as to what splitters you purchase. My father bought a few splitters that degraded his Cable Modem signal before it reached the cable modem. Look to see what frequency range your current splitters are for reference.
posted by ronmexico at 6:15 AM on February 26, 2007

Unpowered splitters will only divide up the existing signal, so if you have a two way splitter each output has half the original signal power, on a four way splitter each output has 1/4 the power, and so on. This should be fine as long as your incoming signal isn't marginal.
posted by TheOnlyCoolTim at 6:46 AM on February 26, 2007

You'll want to get a distribution amp for more than two. TheOnlyCoolTime has it right.

The signal doesn't care if the TV is on or off. The load to the signal is still there if the cable is connected, so seven cables will basically divide the signals seven ways and the cable lengths from each point of separation will further attenuate it.
posted by FauxScot at 6:51 AM on February 26, 2007

I think that it would work fine. After installation, if you find that there is signal degradation you could always install an amplifier for relatively cheap.
posted by i_am_a_Jedi at 6:52 AM on February 26, 2007

IANACRT (I Am Not A Cable Repair Technician)

A few years ago I had 5 cable connections in my house. One was to a cable modem, one was to a digital cable box, and the other three were for "regular" TVs. The modem line was split once (within 50' of the overhead line connection), the digital box was split twice, and the others were split up to four times.

All that is to tell you that all three of the Comcast repair guys who came to the house while I had this setup said that this was the only way to get the modem to work. They told me signal boosters didn't work for the modems and splitting them more than once was a bad idea. But you could split the 'regular' TV signal as many times as you wanted as long as the picture stayed good.

There is a splitter that passes the signal straight through for a cable modem and takes the 'error' (I may be recalling that incorrectly) for a regular TV signal. I used this one successfully on a TV in the same room as the modem.

You may also want to get the best (shielded, thicker) cable you can and replace whatever you can reach. The stuff they are using now is very different from the stuff 20-20 years ago.
posted by mshellenberger at 7:03 AM on February 26, 2007

I have done this for both cable and satellite TV with good results (I was forced to do the former when the cable guy showed up with the additional box I had ordered but knew nothing about the additional outlet I had requested at the same time). The technical term for what you are concerned about is insertion loss, and yes, it is a concern when splitting a cable or other signal. You can measure the signal before and after your modifications, but in practical terms i_am_a_Jedi's answer is the way to go. In my case it worked OK without an amplifier, but when the cable guy was at my house for something else I asked him to measure the signal. It was out of spec so he installed an amplifier for me at no charge and my internet connection and TV reception were noticeably better. Also as mentioned above, make sure that whatever splitters you use will pass high frequencies if you have digital cable or a cable modem. They are only slightly more expensive and are usually labelled for such uses.
posted by TedW at 7:18 AM on February 26, 2007

And despite what the Comcast guys told mshellenberger, my cable modem runs fine over a cable that is split twice (once over a 3 or 4 way splitter) and is amplified where it enters the house.
posted by TedW at 7:22 AM on February 26, 2007

Finally, as mshellenberger noted, better cable will reduce the amount of insertion loss, but depending upon the length of the cable, the strength of the original signal, and a number of other things that I probably don't know about, you may need an amplifier even with quality components.
posted by TedW at 7:24 AM on February 26, 2007

OP didn't ask about cable modems. They DO require bidirectional connections. Splitters are bidirectional, but amps usually are not, though I have designed one that was.

You can connect anyway you want to, but in response to what OP asked, the correct way to do it is to measure the signal being delivered, then split it all you want to until it is at the sensitivity threshold of any given receiver in the mix. At a certain point, it's strength is going to decrease to the detriment of recovered video (or other intelligence) and an amplifier will be needed.

There is NOT an infinite budget of signal that can be spent across an infinite number of receivers. Receivers accomodate wide variations in signal input, but they do each have a minimum sensitivity... part due to design and part related to the indivual set. Go below the minimum, and you lose something. If you need an example, disconnect the cable and see if you see anything. QED.

Home-handymen and cable TV techs are not engineers and just because it 'works' doesn't mean it works optimally. It's analogous to asking a welder to explain bridge design. If they are conscientious and engaged, they will do as above.

I mean no offense to cable installers, and the consequences of insufficient knowledge in this case are zero. Really, who cares if a good signal gets to the TV? Look what you have to watch! Were I OP, I'd ditch the cable and spend the money on bubblegum or something else worthwhile, but that's just me!
posted by FauxScot at 9:53 AM on February 26, 2007

We have one cable box at one end of the house, and the cable splits maybe 5 times up to the other end of the house, and the signal for those is just fine if you're watching tv. It's not strong enough to connect my computer to though.
posted by rubberkey at 12:42 PM on February 26, 2007

All the advice given so far is good. What I would do, assuming that you aren't using digital cable or anything else exotic on the TVs, is two-stage: first, split the line coming into the house in 2, using a very high-quality 1:2 splitter/combiner. ('Good quality' does not mean 'gold plated' from Radioshack. What's important is the frequency range. Make sure it's up to 1GHz.)

Of the two resulting lines, run one directly to your cable modem, with some sort of high-quality low-loss coax. (Again, not Radioshack. In fact, as a general rule, don't buy anything there besides batteries, ever.)

From the other line coming off the 1:2 splitter, run that into a x-way distribution amplifier, where x is greater than the number of TVs you want to use in your house. Then run lines out to all the TVs from there.

At the very least, you'll be able to get all the basic CATV stuff on all the TVs, and you should avoid messing up your cable modem, this way. If you use digital cable boxes or addressable converters (for PPV), then you might need to use an initial splitter with more outputs, because those things don't like being connected downstream of an amplifier. But that's going to divide the signal further, which might mean bad things for your internet service, so I'd recommend against it. You might have to get a technician to come to your house and increase the strength of the signal coming down from the pole to your house, if you do this.

The reason I'm so conservative about the signal going to your internet modem is that it's possible to put it on a cruddy connection, and get slow service, but not have it conk out completely. It's a lot more difficult to test/diagnose problems with the internet modem's signal (without an analyzer, which I assume you don't have) than it is a TV (which will be obvious if it's not getting enough signal, because the picture will be bad on the analog channels). So therefore, I give it top priority.
posted by Kadin2048 at 12:49 PM on February 26, 2007