Diplexers and Amplifiers

[SmashedPumpkins]

I need a little help and it seems that the satellite guys are the ones to come to. I'm at my parents and they currently have cable and would like to use their antenna on the roof. Sorry I know it's not satellite but I believe I should still use a diplexer right? Anyways, the image below is a horribly drawn diagram of how many parents house is wired. The area that the antenna will jump in is where the original cable went to the main room. (You can see we already split it to get into two additional rooms built in our garage. This split is in the attic. Currently a regular splitter is placed in the attic connecting the main room with the cable line and the other OUT port going to an amplifier for the other two rooms.

(Image URL) i39.tinypic.com/6s71va.jpg

Now to be completely honest, I don't know how well the amplifier works. The straight shot from the antenna to the HDTV receives the best results. I placed the amplifier between and we lost several channels. Regardless, we can't really send another cable down the wall and would like to simply connect the antenna into the setup in the attic. My initial plan is to place a diplexer in the attic that has two outs. I'll plug the cable into the satellite IN and the antenna in the antenna IN. One OUT port will go to the HDTV in the main room and another to the amplifier for the two rooms. I'll add another diplexer in the main room as well. (I think) I have several questions though.

First off, with the diplexer, can the cable signal be sent instead of a satellite signal? I've read about power passing and I don't understand what that means and I don't want to break the HDTV. Second, can I simply plug the coaxial cable into the HDTV and let the HDTV separate the signals or is another diplexer required to actually use the signals? Third, with this crazy setup, I'm not worried about losing the cable signal but I'm very worried about losing the antenna signal. I want to keep as many channels as possible. What type of amplifier should I use and where should I place it? (I realize the other 4 rooms aren't going to be able to receive the antenna signal but there's nothing I can do to boost the signal that far or am I wrong on that too?)

So overall, if you can advise me on what would be the best way to accomplish this and still keep a strong signal from the antenna I would be very grateful. Thanks!

EDIT: The cable provider requires a small Comcast box at every TV. To change the channel you actually change it on the Comcast box. The TV channels always remains at 4. (I wasn't sure if this means a different frequency was being used along the cable or not. I was kinda hoping because I heard cable and antenna use the same frequencies)

EDIT2: The more I read the more I don't think this will work. It sounds like cable uses most of the spectrum pretty randomly depending on where you live. :/

 

[TimberWolf]

You need a combiner, a diplexer won't do anything for you.

Even then, picture quality will probably suffer using your existing lines.

Have you tried just an indoor ant on the main tv?

 

[upsss]

You cannot combine (no matter what you use, splitters or diplexers) OTA channels with Cable, feed it to the Cable Boxes and expect to receive the OTA channels out of your Cable Boxes. What you can do is combine the output from your Cable Box with the OTA antenna on each TV (using splitters). Then you would tune the TVs to channel 4 to receive the Cable channels by tuning the Cable Box or tuning the TV to the appropriate channels to receive the OTA channels.

Now my question, why would you want to pickup your local OTA channels with an antenna? Don't you get these channels from our Cable company anyway?

 

[DishSubLA]

Just some foundations to help you along:

Cable ANALOG a bit off frequency from OTA, so, practically speaking, Cable ANALOG and OTA are pretty much the same frequencies and they will interfere with each other.

If your service is part of the DIGITAL cable spectrum, then only Amps, splitters, etc. rated for the digital spectrum will work. If you place equipment NOT rated for digital spectrum, you will LOSE many channels.

On the digital spectrum, many cable companies use Switched Digital Video (SDV), meaning that the request for the channel MUST come from the cable box or an external SDV adapter. Please google or wikepedia Switch Digital Video for info.

In short, messing with cable TV service today aint what it used to be. One MUST be pretty well informed about the particulars of their CATV service, or one will have a very tough time getting any sort of customization to work as expected.