It does not have to be RG6. Belden for example makes a very nice RG11, RG59 swept to 3.0 Ghz and even a smaller diameter coax for patching that is swept plenty high to accomodate cable modem services. RG/11 will provide less loss than RG6, RG59 and the smaller stuff will be more lossy. Depending on the length of run, one needs to take that into account when designing the system.
There is nothing inherit to a splitter that will cause a problem with it in front of a modem. Unless you live at the headend, that signal is 'split' and 'tapped' many times before it arrives at your house.
There ARE two things regarding splitters that WILL make a difference with your cable modem. Those two things are the bandwidth of the splitter itself, and the attenuation associated with the insertion of the splitter.
Keep in mind this is all two-way radio frequency stuff. On my particular system the cable modem downstream signal is about 650 MHz and the upstream frequency is about 24 Mhz. Now, for the system to work, ANY device you install in the line must be able to pass signals in excess of 650 Mhz. Decent splitters should have a range up to 1 Ghz. Many cheap and/or old splitters were designed for broadcast signals or early CATV systems that did not have channels in the 650 MHz range so they may only pass signals up to 550 Mhz or so. So, first and formost, any splitter you use needs to pass everything you are going to send through it. Secondly, splitters are very lossy. A 2-way splitter will make both signals go down 3 dB. 3-way and 4-way splitters are even more lossy. So you can see that you could easily reduce the signal by 1/2 just by popping a splitter in there. However, it is done all the time. Many DOCSIS modems allow you to point your web browser to the modem (my motorola bitsurfer is at 192.168.100.1) and see what the signal strength is of the downstream signal. When I installed mine, the cable technician and I experimented with different signal levels. We found that putting a splitter in first, sending one port to the modem and the other port to an 8 way amplified splitter for the rest of the house was too much signal for the cable modem. It actually performed better when a 6 dB attenuator was added before the modem.
I believe your best solution is to run a new piece of quality (I prefer RG/6) cable from the CATV interface to your basement patch panel. That way, you can put a splitter in out there and get as much of the signal as you can downstairs. From there, you can work with different devices and get the signal level you need to make your cable modem work. Like any radio, the modem is expecting a certain level of signal to function properly. You can either experiment while looking at the web interface to get that correct level or put a signal strength meter on it and adjust it that way.
Hope that helps!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com
