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Published: 2007-10-01 - 08:30:00
Home Theater : Ask The Expert

Cable Modem and OTA HDTV Antenna on Same Coax - Good Idea?

By Chris Boylan

Question:

Hello, Big Picture Big Sound,

I ran across a question/answer on your site here.

In the answer you mention that the cable TV signal will interfere with the antenna signal (and vice versa). I am looking to use an antenna for TV service and a cable modem for internet service (I dont want and am not getting cable TV service from the cable company). Will the cable internet service interfere with the antenna signal if they are combined on the same coax line? The reason I ask is because I would like to put a TV in the same the location as the cable modem.

As a follow up question, is it OK to combine a MoCA network with these two signals, I'd like to setup a media center PC but use MoCA to distribute the media throughout the house?

If it will work do you have a suggestion as to a coax splitter/combiner I can use to put both signals on the coax network? I have 7 coax jacks in the various rooms throughout my house.

Thank you,

-Zach



Answer:

Hello, Zach,

Thanks for your question. If you specifically tell your cable provider that you do not want cable TV service (only cable internet) and ask them to filter out the cable TV channels, then you should be OK combining cable modem and antenna broadcasts over a single coax cable. The filter or "trap" would filter out the TV frequencies from the line, but leave the frequencies used by the cable modem intact.

Without this filter in place, the cable TV signals will interfere with the OTA antenna signals, causing picture degradation. With the filter, you should be able to put the cable signal and TV antenna signal into a simple (high bandwidth) splitter/combiner, and plug this feed into your cable distribution system. You'd then be able to use any of your 7 coax cable jacks for the antenna signal, and use any one of those for the cable modem. If you're splitting the signal 7 ways though, then you will probably need a decent amplifier. Make sure to get an amplifier that is bi-directional as this is required for cable modem use (must be able to send and receive).

For a splitter/combiner, use something high quality and high bandwidth like this one from Monster.

For a signal amplifier, there are some good inexpensive ones from Motorola and Channel Master (among others). We've had good luck with these ones:

The Motorola BDA-S2, BDA-S4 and the Channel Master 3044 each include a built-in signal splitter, so you can save yourself from having to buy a separate splitter. All of the above include high output, low noise amplifiers and support return feeds for cable modems and interactive features such as PPV.

If it were me, though, I'd keep the cable modem and antenna feeds separate. You're only going to be using the cable modem in one room, so I'd just run the cable feed right into that room with its own jack and keep the antenna cables separate. Any time you introduce diplexers, combiners or splitters, you're going to have signal loss, and with signal loss you can have picture quality degradation (or network outages).

As for your second question, MoCA (Multimedia over Coax Alliance) networking products operate above 850MHz so they should not interfere with an antenna signal on the same coax line.

Hope that helps.

Regards,

-Chris

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