Broadcasting 720p/1080i signals over RG6

Discussion in 'Playback Devices' started by Richard E Jones, Jan 12, 2005.

  1. Richard E Jones

    Richard E Jones Auditioning

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    I had intended to try to keep video sources in one room and broadcast them via distribution amps and a modulator onto a RG6 network in my house. I think this will allow me to broadcast a DVD or HD TV source from the one location to all RG6 points in the house. First question - do people do this? Second question, if it is a 480p/720p/1080i source and there is a suitable display at the other end can I modulate the source onto the RG6 at a specific frequency and then tune the display devices and receive the HD signal properly?

    BTW this solution is not for the cinema as I've used multiple RG59 for component video for that room - its the other areas of the house - family room, lounge etc where I want to achieve this.

    Cheers
    REJ
     
  2. ChristopherDAC

    ChristopherDAC Producer

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    When you say "modulate" and "broadcast" -- are you talking about taking analog component outputs and RF-modulating [FM or AM] them each onto a separate carrier on one cable, or using a distribution amp to send them as baseband analog signals over three separate cables, or faking up an ATSC digital broadcast stream and sending via OTA or CATV transmission protocols around your house? Any one of these is possible, but except for the 3-wire solution they would require some heavy-duty professional equipment. There are other options -- Serial Digital [probably fiber-optic], or HLO-PAL or TCI [for 1035i only, and impossible to get the equipment I think]; but in any case it'll be trouble. You might look into building a LAN to stream HD-MPEG and using dedicated HTPC terminals all over the house, but that's pretty bad too.
     
  3. Richard E Jones

    Richard E Jones Auditioning

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    Thanks for your response Christopher - yes analog component outputs from a HD source. Not being technical I am not sure how to respond to your next question! However, I can describe the physical aspects of my cabling if that helps. I have a video hub and no amplifiers at the moment. Connected to the hub is a free to air TV antenna. Also connected to the hub are individual RG6 connections that go to various points in the house - one cable per location. It was my understanding that a number of composite video sources and associated audio could be transmitted onto this RG6 "network" (at prescribed frequencies) and therefore allowing all TVs to share such composite video sources located centrally. So the question I posted is an extension of this. I was wondering if there was a way of taking component video and associated audio and "modulating" that onto the RG6 network and if so, could a HD signal be sent as HD (720p or 1080i) in the same way. My apologies if this still doesn't make sense!

    At each RG6 outlet I also have a cat5e UTP cable as well - these are not in use.

    Cheers
    Richard
     
  4. David_Rivshin

    David_Rivshin Second Unit

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    The short answer is yes, it's possible, but it will be so expensive that I doubt you'd go for it.

    Long answer:
    Composite + stereo audio all combined onto one cable is exactly what CableTV or analog broadcast TV is. This combining process is the operation that your VCR or other device does when it outputs onto channel 3 (for instance), and is often called modulation (even though it's probably more accurate to call it frequency division multiplexing). Each channel in this scheme uses about 6Mhz bandwidth IIRC, and you can 100+ channels this way onto one (relatively) cheap RG59 cable.
    You can easily find modulators which will take multiple composite+stereo signals and put them onto various channels for whole house distribution. They aren't cheap, but they aren't too expensive either.

    HD signals contain alot more information, and so require much more bandwidth. IIRC we're talking in the range of 50MHz for each of the 3 signals, or around 150MHz total. So you might be able to fit around a dozen "HD" channels onto a high quality RG6 coax cable. I doubt anyone has ever made a device to modulate HD component, and if they did it would no doubt cost an arm and two legs. Of course you'd also need a demodulator on the other end to split that signal back into component, and that wouldn't be cheap either.

    You should note that the modulation/demodulation steps will slightly degrade the signal quality, even with the best components.

    HD broadcasts are accomplished via a standard known as ATSC. It takes that same 6MHz bandwidth used for normal NTSC broadcasts, and squeezes HD signals into it. It accomplishes this by digitizing the signal, and then MPEG2 compressing it. I'm sure you can find an ATSC encoder, but it will probably cost a few thousand dollars. ATSC tuner's run in the range of $200-$300 if you don't already have one for each display.

    The easiest way to distribute HD video would be to run 5 cables to each locations (3 for component video, and 2 for audio), and buy or build a distribution amp. You can even get cables (Canare has some I know) with 5 coax's in one bundle. A component distribution amp would probably be hard to find, but someone out there might have something. I'm thinking it might even work if you took 5 good cableTV distribution amps (one for each cable), might be worth a try since they are alot easier to come by.

    -- Dave
     
  5. ChristopherDAC

    ChristopherDAC Producer

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    Dave hath the right of it.
    What you want to do is technically possible, but I've never heard of it being done -- the closest I can think of is the MUSE cable-TV experiments in Japan. If you don't want to run all the separate wires, I seem to recall that there is a fairly standard way of using a 15-pin VGA type connector and the appropriate cable to carry all those signals, and you should be able to get video distribution amplifiers to suit. I for one would not try to use CATV amps, because baseband video needs to have good frequency response down to DC [or at least 60 Hz] and any RF amp typically has a roll-off below the lowest TV carriers [~45 MHz].
     
  6. David_Rivshin

    David_Rivshin Second Unit

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    A VGA cable is really no different than running separate coax lines. The cable would be thinner overall, but each signal wire in a VGA cable is significantly thinner, and wouldn't provide as good of quality over long distances. High-end solutions actually break out the 15pin VGA connector into 5 coax lines for the RGBHV signals, and use coax for the long-haul. Many high-end computer monitors have 5 BNC inputs for that purpose (often in addition to a normal DB15 VGA input).


    Oops, you're absolutely right. Oh well, it was a thought.

    I suppose the only way of getting off cheap would be to build your own distribution amp. If the number of used outputs stays constant, then all you need is to amplify the incoming signal to make up for the signal loss of splitting the signal. Anyone handy with a soldering iron and basic electronics skill could build such a device. Biggest problem would probably be physically fitting such a mass of connectors in a reasonably sized box.
    (Disclaimer: I've never actually built a distribution amp, so I may be missing something, but it seems like it should work pretty easily.)

    -- Dave
     
  7. ChristopherDAC

    ChristopherDAC Producer

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    I'm just saying that, if actually running 5-7 cables is a problem, he might be able to save trouble with a single jacket. The same would be true, of course, of putting the separate cables into a conduit and pulling the conduit rather than the individual cables -- there's less danger of the stuff snarling or snaking all over everywhere. And as for the distro amp, with all the trouble the audio people go to making an amp -- though this is a line-level and not a power amp, so it is a little easier -- phase linear and flat with respect to frequency response over a measly 20 kHz, do you think somebody with a soldering iron is going to have an easy time making something for a 30 MHz bandpass? You may be on to something, though. I know audio preamp chips are available, if Mr. Jones is willing to trust his sound to ICs, and I think there are video-frequency op-amps now, which really would be a soldering-iron solution. They could be wired up as unity-gain voltage amplifiers [buffers] I think, or a little more than unity perhaps to compensate for line losses but those will not be large, it is simply the problem of driving into several 75 ohm termination resistances instead of one wherewith we have to deal. Once upon a time, equipment with audio or video inputs used to have two inputs, "pass-through" high-impedance to allow daisy-chaining and "termination" for the end of the line. I haven't seen anything like that in new hardware, though, so I guess there's no getting away from distibution amplifiers.
     
  8. Richard E Jones

    Richard E Jones Auditioning

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    Guys, thanks very much for your advice and suggestions. I think I'll stick with SD!
     
  9. jimkent

    jimkent Auditioning

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    Folks, I've been searching for a solution to this problem for years now. I called major developers of Analog Modulation products, I've googled, I've done it all. The problem (supposedly) for putting HD on a channel (other than bandwidth) is the copy protection and all the other things that gets put onto the signal. According to these manufactures. That's why they don't do it. It's to pricey for the consumer market.
    But! Look at what I just found:

    Send Ethernet over RG-6 or RG-59 Coax - CAT-5 TO RG-6 CONVERTER

    It puts Cat5 signals on RG6. They make both Passive and Active versions of Component -to- Cat5 converters. so, you see where I'm going with this?
    TV->Component->Cat5->RG6 --------- RG6->Cat5->Component->TV

    It's a thought. [​IMG]
     
  10. Stephen Tu

    Stephen Tu Screenwriter

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    Component->cat 5 may be the right idea for the original poster, who has cat5 runs. Don't have personal experience with this so I don't know how well this works. Might search over at avsforum which has an AV distribution subforum for more specific info.

    But the ethernet on RG-6 idea is barking up totally the wrong tree -- that's for sending digital computer ethernet network packets, not analog component video signals. Cat5 is just a wire type, it can be used to carry analog signals or digital signals, the component->cat 5 is still sending an analog signal, not encoding the data and sending it as a digital TCP/IP stream.

    For HD digital QAM modulated on RG-6 I think I've got all the equipment necessary sitting in the couple labs next to my office. I also think the total cost of the equipment is probably > $20k [​IMG]. So for home use I think I would stick with media center extenders and a LAN, I'd prefer that over analog distribution which IMO is not the direction of the future.
     

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