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Can i split the coax cable going to my cable modem to attach a TV there ?

Usually yes, however it is not a good idea to do so. Every splitter on the cable between the can and your cable modem reduces signal strength (by at least 3db). Also, mistakes in home wiring can cause ingress in the upstream channel for all users on that upstream.

If you must split the cable going to your cable modem, you should use either a tap (loss only on one end, going to your TV), or high grade 2GHz splitters, and because of the lower signal level the modem might not synch at all, or you might experience some packet loss and speed degradation. Depending on your installation, there also might be some filters on the line preventing the operation of both TV and the cable modem on the same cable.

Notes: It may be a good idea to check the signal strength on your cable modem to determine whether a tap or a splitter is better for you - a tap will only incur signal degradation on one leg (-6db), while a splitter will incur signal degradation on both legs (-3.5db).

  User Reviews/Comments:
by anonymous - 2008-05-16 11:12
please everyone remember most cable systems aren't 2ghz systems yet the downstream bits usually run between the 500 and 750 mhz range as the upstream is ususally between 5-125mhz depending on the system 5-1000mhz splitters are what the cable industry uses. if you want to split for a tv just be sure to verify outside that the cable coming into your house is split the cable modem first most good splitters tell you how much they lose on each leg for example 2 way splitter 3.5db cumlative across the bandwidth on each leg or a 3 way splitter balanced 5.5db on each leg of lose unbalanced 3.5db on one and 7.0db on the other two. in a typical sitaution you will see a two splitter one leg feeding your cable modem the other leg feeding another splitter. remember the loses on the splitter add so in you have one two splitter feeding another two way splitter and they both lose 3.5 culmative then the total is 7.0db. the fcc says a minimum of +5 should be at the house high and low band. you may also seeing depending on the modem a signal screen shot at
by anonymous - 2008-10-06 23:38
A littel more info on splitting your coax.
Disclaimer: I work for a cable company as a high-level tech.

First of all, most ISP's/TV companies now are getting into phone as well and are using more spectrum, so a 5-1000 splitter is a must (up to 2000 optional, it won't hurt) & get a good one. Always use the heaviest grade coax (better shielding) and ALWAYS the screw connectors, never the easy 'push-on' ones.
Next, a lot of TV equipment, like old VCR's, can introduce noise' into the coax line, on frequency ranges that didn't used to carry any real signal information. Many cable boxes (especially if you use a Video On Demand service) need to communicate upstream as well to order content.

So the total spectrum (5-1000) is split up with most of the TV content in the lower portion, and the very high end is usually used for data (750-1000 much of the time). But some equipment might still pollute the upper area. Therefore most ISP's have started adding filters to each outlet to keep this out of the way.

For example, much of the time you will have the main feed to the splitter, then the line that goes to the TV will have a filter that prevents any signal passing in the upper 750-1000 range, so the TV equipment won't pollute the data stream for the modem. Side effects of the pollution include packet loss, latency, or straight up loss of bloc sync.
Be aware that the filter will also act as a resistor, which can affect your signal strength. Be very very careful if you decide to add your own signal amplifier, as they tend to introduce/amplify noise as well as signal, and if not used properly can burn out your modem/TV equipment.

All in all, it's often not a big deal to split your cable, especially if you have a long piece of coax you can take out of the line when you add the new span to the TV/modem. It certainly won't damage your equipment to try it, but if it doesn't work now you know a litte more about why.
by Midnght_J - 2010-02-26 16:30
thx for the info
by Aaron - 2015-10-08 19:29
Thanks for the education!
I am stuck with my setup. Maybe you can help me.

I currently have Roadrunner with Time Warner as well as the cheap cable package for $10
I also bought an attic antenna to reach 100 miles and pick up my Browns games on Sundays.
How do I set this up so that I can switch between my time warner cable and the attic antenna WITHOUT losing my internet when I switch to the attic antenna?

I tried to split the connection but that did not work. Any suggestions would be greatly appreciated.
by Philip - 2015-10-12 06:40
The easiest way would be to run two separate coax cables... One from Time Warner to the cable modem and from there to your computers. The Time Warner cable TV can be connected from their box to the TV with a component/composite/S-Video or any other type of cable.

That way, you can free the coax input on your TV for a separate direct run from your OTA antenna.

There are other options, but this is the most straight-forward one imho.
by Networking Noob - 2015-12-08 18:40
Aaron, Philip is correct. this is the best solution. don't forget to connect a digital converter box between the second coax and the TV input if you don't have an HD TV.

This is exactly how I have my house setup, and I use WiFi to connect my computers to the modem as we don't use desktops.
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