Split cable to run high-speed internet and TV ?
 

I have Comcast cable internet and TV, with various drops around the house including one in my office.

Sometimes it would be nice to be able to watch TV in the corner of my monitor as I work. I do not have a TV tuner in my computer but it should be a trivial matter to install one.

Can I just split the cable at the wall jack then run one cable to my cable modem and the other to a TV tuner card? Or is it more complicated than that?

It works just like that, with one caveat. If you're trying to watch HD, and you have a lot of TV's in your home, you *may* need a signal booster for the house. I had this problem and it was easy to fix-it just drove me crazy for a while with stations that wouldn't hold their signal and HD that was constantly cutting out. If you need to go this way, be sure you get a booster that handles both the incoming and outgoing signals that Comcast uses. I have a Motorola unit-can't remember the model number. If you need to go this way, PM me and I'll get it for you.

Also, make sure the splitter you use is a good quality one.

I split the only line coming into my apartment for the purposes of TV & Internet. They make a prioritized splitter which looks like a T. I gave the prioritized signal to the internet because it tends to have a lower threshold for noise.

I believe you are better off having one multi-way splitter instead of a daisy-chain of two way splitters. You will get less signal loss using a four or five way splitter once than multiple two way splitters. You also need to make sure the frequency response is high enough (up to 100,000 Mhz I think). Boosters may not work as the signal has to go both ways for internet, converter boxes, etc.

Quality of the cable can make a difference too.

Quick solution - put a two way splitter in the closest location and see how it works. If no problems you are done.

If something stops working, look at a different solution.

When my house was wired for cable TV they set-up a chain of two-way splitters. I had to put my cable modem and wireless router on the first splitter. The one TV is on the last splitter.

Putting both on the last splitter (which required yet another splitter) caused intermittent loss of connectivity and static buildup ruining the TV signal for the lower-numbered channels.

This is why I got DSL. :D :D

Can I suggest that you buy a slingbox instead of a tuner card. You can watch it on your network anywhere in the house. If you have a wireless network it is even better.

Point your browser at HTTP://192.168.100.1 if you have a Motorola Cable Modem. That'll bring up the internal status page. Check the Signal Level page and write those figures down. You want the downstream SNR to be above 30dB (or close), and the downstream power level to ideally be between -8 and +8dB (although -15 to +15 will work but not ideal).

The most important figure is the upstream power. This ideally should be below 50dB but up to 53dB is acceptable. 55dB is generally the limit... and indicates problems with the cable network impeding the return path. Upstream SNR (Signal/Noise Ratio) should be 29dB or above. Also, run a speedtest at someplace like dslreports.com and get an idea for how fast your connection is (this will vary but shouldn't vary too much... what you're looking for is a big repeatable drop on downstream *and* upstream speeds after any changes).

Now that you've got your baseline, stick a garden variety splitter in the path and connect everything up. Go look at those numbers again. As long as you haven't gone below/above the mentioned levels, you are good to go. Run a few speedtests (I like dfw.speakeasy.net, which then allows you to use any of several tests around the country) and if you don't have any major changes in the quality of your connection, you needn't do anything else.

If the splitter DOES cause a problem, use a tap (proper name: Directional Coupler) instead. You'll have to order one of these, it's not something you'll find at a Radio Shack. It's basically a splitter that has a ~1dB loss on one output and a ~6dB loss on the other. They're for daisy chaining outlets together (as in a hotel), but also work for our purposes as the cable modem feed is almost lossless. For TV, you can compensate with an amp if it's snowy or you have digital dropouts. For cablemodems, you really can't. I use one and it works perfectly. Here is one source. Haven't used 'em, they're just what came up first in google!

One further issue. Amplifiers DO NOT help cable modems. Almost all only amplify the forward path and pass the return without amplification. They also add noise. So if you have an amp, it's best to put the modem ahead of the amplifier if possible. If you don't have enough signal prior to the amp, call the cable co. It's their issue and they need to fix it.

Also, when splitting, make sure all connections are good and tight. I've had lots of signal loss issues when connectors became loose over time.

An amplifier *might* help a cable modem. The downstream signal (cable headend to home) is usually carried in the same frequency range as the video, 54 MHz up to 600 to 800 MHz, and usually near the upper edge; the frequency of the upper edge depends on the specific cable system. If the downstream cable modem signal is right at the upper edge, and if the cable signal strength "rolls off" at the high frequency end (decreased amplitude), then an amplifier could help the cable modem signal. The upstream signal (home to cable headend) is carried in the frequency range below 50 MHz, and indeed amplifiers cannot help the upstream signals.

Amplifiers tend to cause more problems than they solve. Almost all are passive return and have an insertion loss penalty that can cause far more problems than the downstream amplification potentially solves.

Active return amplifiers exist, but require much more careful setup to avoid causing massive problems for everyone on the node. Whereas a downstream amp only screws you up if it's not set up correctly, an upstream amp that's misconfigured will result in a visit from the cable co in fairly short order. I've heard of an 'automated' active return amp that is self-controlling but haven't seen one yet.