DTV and antenna in one downlead

[bigblk55]

I live in 29582 zip code. I have direct tv but I want to add an antenna to get local stations and use the same coax cable. My dtv receiver has an off air input. Can I use a diplexer and combine the signal, and then use one to split the signal at the receiver and then go in to the off air input? I cannot run a second cable because it would require drilling another hole in a masonry wall. Any help is appreciated. Also. I plan on using a MS 2002 winegard mounted in the attic. Here is my location

http://www.tvfool.com/?option=com_wr...9fbe0ea6d89c46

Dennis

[mtownsend]

I'm not sure if you will be able to cleanly diplex the signals onto a single downlead. I'm not an expert on DirecTV signaling, but my understanding is that the coax signal is being carried at 950 and 1450 MHz. The top of the TV spectrum is at 700 MHz. Furthermore, the LNB on the dish needs to receive DC and 22 kHz signals to select between different frequency and polarization modes. The MS-2002 needs its own DC power on the same coax.

A single coax solution appears to be out of the question.

BTW, an MS-2002 in the attic will probably only be able to get the channels in the "green" zone on your list. The low intrinsic gain of the antenna (not counting the gain of the built-in amp) and the signal degradation you get from being indoors means that you aren't likely to get channels lower down on your list.

[bigblk55]

I thought the same thing until I found this:
http://www.satelliteinstaller.com/sa..._diplexers.htm

Maybe it will work with an antenna without an amp.

Has anyone had any experience with this antenna?

http://www.dennysantennaservice.com/...guarantee.html

Thanks for your reply.

Regards
DH

[mtownsend]

If your TV antenna does not require any power via the coax, then there's a chance that this *might* work. You would need to hear from someone who's an expert on DirecTV to make sure that the signal and power passing between the LNB (on the dish) do not interfere with the VHF/UHF OTA signals and vice-versa.

Remember that there are power (DC) and control signals (~22 kHz) passing up to the dish and downconverted satellite signals (~950 - ~1450 MHz) coming down from the dish. OTA TV signals occupy 54 - 806 MHz (now actually 54 - 698 MHz after the digital transition). In order for the diplexors to work, they must be able to combine/separate the signals at both ends of the cable and keep thing isolated enough such that the signals from one system do not cause problems for the other.

You need to be careful about where the DC power is going because you don't want to send power into your TV's RF input or any other places it's not supposed to go. If the power is going anywhere other than the dish itself, you might end up with insufficient voltage to power the dish. It's also unclear whether any of this will interfere with the 22 kHz control signals.



You might want to check around for independent confirmation from people that have successfully done this (not just from the people trying to sell the diplexors). As an RF engineer, I think the risk of cross-interference is high, but I would not go so far as to say it's impossible to make this work.



As for the antenna choice... You have stations coming from many different directions. If you go with a directional antenna like the one you pointed out, you will only be able to pick up one group of channels at a time, and you will need an antenna rotator to move the antenna around for the other channels.

The good thing about directional antennas is that you'll get more gain out of them, so you can pick up more channels down into the "red" zone on your list, assuming you've used an antenna rotator to aim it correctly.

If you go with an omni-directional antenna like the MS-1000 (non-amplified version of the MS-2002), you can pick up channels from multiple directions simultaneously, but the antenna gain won't be so good. With an omni antenna, you'll probably only get channels in the "green" and maybe some "yellow" zone channels.