How many times can I split my cable line? There is only 1 cable line into my house which I have split into two - one going to my digital cable box and the other going to my modem. Can I split it again (for another tv) without sacrificing performance?
Shouldn’t be a problem. Just be sure to use good RG6 cable and a good splitter - eg: one that’s rated at something like 5-1000 MHz. Cheap cables or cheap splitters can cause ghosting and bad reception of the higher-numbered channels.
Another bit of advise is to feed the cable modem directly from the cable TV company’s splitter, and route the other side of their splitter (the side that is currently feeding your one TV) to your splitter to feed the TVs. Putting another splitter in with the cable modem can cause erratic connections or lowered connection speed.
A typical 2-way CATV splitter will cause a loss of -3.5 dB, meaning about 44% of the original signal is getting thru. A 4-way splitter (or a 2nd 2-way one) will cause a loss of -7dB, so only about 20% of the signal is getting thru at that point. And RG-6 cable will lose about -1dB for every 20 feet. Note that it’s the cumulative total that matters. A pair of 2-way splitters (-3.5dB each) + 40’ of cable = -9db loss, or only 12% of the original signal strength getting through.
So is that a problem? Depends on the strength of the original signal, which depends on how far you are from the last cable feed amp, how well the cables in your neighborhood were installed, and how strong a signal the cable company provides. Also depends on how good your TV is at working with a weak signal. All of that can vary a lot for different locations.
The best thing to do is just try it. It’s easy enough to fix if it doesn’t work. If your TV’s don’t work (lots of snowy picture and interference), all you have to do is put a video amplifier in the circuit to compensate for the signal loss of the splitters & cable. Good quality video amps (+10 to +15dB gain) are available at reasonable prices (under $100) from hardware stores and Home Depot or Lowes.