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Hooking up a DTV converter backwards

Discussion in 'Electronic Repair' started by [email protected], Feb 3, 2009.

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  1. Guest

    OK, I am not buying this, but I read in a discussion group that if a
    person hooks up a DTV converter backwards, the result will be an
    analog signal that is broadcast into the home or to any tv within a
    small distance from the converter.

    First it would take some serious modifications to connect it
    backwards, then I dont thing these converters are actually
    transmitters.

    But I'll remain open minded until this is proved wrong.

    I also heard that a DTV converter can be connected to a computer
    monitor rather than a tv. This one I'll consider a good possibility,
    IF they make monitors with a VIDEO input, (as in RCA connector). I
    have not shopped for a monitor for years, so maybe the new ones do
    have these connectors. My old CRT monitor only has the standard SVGA
    input connector that if I recall, has 15 pins.

    So, maybe there is some truth to this, although an external sound
    system will be needed for the audio, which I'm sure any stereo
    receiver or amp will work.

    Anyone know any truth to these things?

    LM
     
  2. #1: Bullshit, requiring no more explanation to anyone who knows anything
    about electronics (inputs are inputs, outputs are outputs, etc.).

    #2: True. Video is video. (S-video, I b'leeves, although I could be
    shown to be wrong on that.)


    --
    Personally, I like Vista, but I probably won't use it. I like it
    because it generates considerable business for me in consulting and
    upgrades. As long as there is hardware and software out there that
    doesn't work, I stay in business. Incidentally, my company motto is
    "If this stuff worked, you wouldn't need me".

    - lifted from sci.electronics.repair
     
  3. This is like saying that if you shine a bright light on a fluorescent tube,
    the tube will produce an output voltage.

    Broadly speaking, an input (output) cannot magically become an output
    (input).
     
  4. Rich Webb

    Rich Webb Guest

    Well, one could certainly take the RF output from the converter box and
    run it into a splitter and then to two or several separate analog sets
    over coax.

    One could also connect that RF-out jack to an antenna instead and so
    "broadcast" it. However, transmission antennas require more thought and
    design than just hooking up an old set of rabbit ears. And, by operating
    an "intentional radiator," FCC issues come into play. Unlicensed
    transmitters are frowned upon, although there are exceptions based on
    the band being used and the output power.

    If you want to run multiple sets off of a single converter box (quite a
    reasonable thing to do) then the coax + splitter (possibly an amplified
    one) is probably the best way to go about it.
     
  5. Hi!
    Not really. Not only is there the 75 ohm coaxial connector for input, but
    most of them also have an identical looking connector for RF output in
    addition to composite or S-Video output.

    That RF output is a small, extremely low power modulator that outputs to TV
    channel 3 or 4. It would not be impossible to hook it up improperly, get
    some digital TV reception from the length of coaxial cable connected to the
    antenna input and have that be rebroadcast "out" to the antenna, where it
    might travel a short distance and be receivable by other TVs. The harm it
    would do would be minimal and the cable swap would probably be corrected
    quickly when the person doing the work discovered their own set did not work
    properly.
    That depends upon the monitor. None of the couple eligible converters will
    offer anything like that, although some higher end models might. Some
    monitors can accept composite or S-video input alongside the VGA or DVI
    inputs they also have.

    William
     
  6. Hi!
    should read "coupon". Guess my mind was somewhere else.

    It's also worth mentioning that one way you could watch TV on your computer
    screen is with a TV tuner expansion card. Some computers have these
    installed from the factory, or you can add one. I have been using a Zenith
    converter box with my ATI TV Wonder PCI, and it works fine...although right
    now it's hooked up to the RF modulator on the converter and so I don't get
    stereo sound any more.

    Dedicated boxes have also been sold with a TV tuner at one end and a 15-pin
    VGA connector at the other. I have one of those as well. It actually "taps"
    into the keyboard cable and TV can be called up with a special keystroke.
    It's also possible to watch TV in a window with it, as it comes with some
    software that draws a window of a certain color that the hardware will find
    and place the TV image in.

    William
     
  7. Guest

    That sounds like a good idea. I wonder how far it would transmit?
    I am on a farm, and very far from tv stations. It would be nice to
    broadcast from the house so I could watch tv in the barn or garage.
    Right now I can barely get stations in those out buildings, using only
    rabbit ears. I cant justify putting roof antennas on all buildings.

    The buildings are all within a maximum of 250 ft from the house.

    Of course for what you are saying, I'd need 2 antennas on the house,
    one to receive, and one to transmit, right?
    Those are all RCA plugs, right?
    It used to be yellow was video, and red/white audio L+R.
    These says they have a plug of almost every color under the sun.
    I have never learned what they are all for.
    By the way, you mentioned 75 ohm tv coax. I'm not planning to do it,
    but what would happen if someone used some 50 ohm coax made for CB
    radios (and I think Ham too)?
    Just curious because they both look darn near the same.....

    LM
     
  8. Guest

    I thought thats what you meant......
    I've seen those advertised, never seen one in action though.
    I've heard that you can put the tv picture in a small window on the
    desktop.
    That's a pretty wild sort of thing. I never heard of such a device.
    I've also heard some of the newer tv sets can be used as a computer
    monitor. But I cant understand how to connect them. Does the tv have
    a vga connector or so the newest computers have a AV outputs? My 8
    year old computer dont have any of that stuff.

    I've always wanted to take a laptop computer to a friends house, plug
    it into their tv, and show them my digital photos. If they got a
    computer, I can just use their monitor, but for example, my elderly
    relatives dont have computers, and I dont print most photos like they
    did in the film days.
     
  9. Hi!

    (TV tuner PCI card)
    They actually work pretty well, for the most part. And most of them
    can record. Some even have hardware assisted recording, using a
    dedicated processor on the card.

    You can watch the TV in a window, put it on your whole screen, or in
    the case of the ATI TV Wonder I've got, use "video wallpaper".

    I recently bought one that has an ATSC (digital broadcast TV) tuner
    built into it. It works nicely.

    (dedicated TV box for computer)
    It can work either way. Recent TVs typically have high quality display
    that are also suitable for high resolution computer use, so they may
    have a VGA, DVI or other computer display connector on board.

    For older TVs (which may not be so good for high resolution use), the
    computer may have a TV output on its video card.
    Many laptops have an onboard TV encoder that can display a picture on
    a regular TV. You might need an extra cable to be able to use it,
    though. You would also need to be able to turn it on, something that
    would be an option in the control panel software for your laptop's
    video system.

    William
     
  10. Hi!
    I don't think it would get any further than maybe 50-100 feet from the
    antenna. Anything in the way might reduce that range significantly.

    And it's not really legal to do it, although if you are out in the
    middle of nowhere with nobody around I doubt anyone would mind or even
    notice.

    My only real concern is that the little RF modulator in your converter
    box might not be up to driving an antenna. That risk is likely to be
    small, however.
    Yes, ideally. I've never tried it.
    Composite video comes on a yellow plug with this type of equipment.
    Audio right and left are red and white as you said.

    S-Video is a four pin round connector with a key so you can't plug it
    in the wrong way. It doesn't provide audio.

    The other ones (green, blue and others) are for use with higher end
    equipment and typically separate out the color information and sync
    signals. They should be labeled as to what they do, or you'd match the
    colors with the plugs on your TV.

    (This is a US-based perspective on the subject. If you're outside of
    the US, you may have other connectors to choose from, such as SCART.)
    For something non-critical and simple like this, it would probably
    work acceptably well.

    For the buildings on your farm, you might be better served by a "video
    sender". These have been on the market for a while. You plug one into
    the device playing video, and plug the other one into a TV. These are
    legal, operate in the 2.4GHz band for the most part, and actually
    offer a pretty good operating range. Some even relay remote control
    signals to the device providing the video.

    William
     
  11. Twayne

    Twayne Guest

    Have you seen/tried that? I'd expect standing waves to immediately
    trash any chance of anything being radiated and under the right
    circumstances blowing the ouput components.

    Interesting concept, but ...
    BTW, reason I'm fairly sure is my neighbor tried to do something similar
    with an 80 dB amp from RS. It did a whole lot of nuttin' and then
    wouldn't work when he tried to put it back to watch TV. I'm guessing
    that he built a great standign wave generator<g>.
     
  12. Gnack Nol

    Gnack Nol Guest

    While hooking up many of the old discrete UHF tuners defiantly worked
    backwards as a vhf / uhf up converter. Analog modulators had no way of up
    conversion since they contained no descrete local conversion oscillator /
    mixer to mix the signals. This I know having played with the modulator
    modules that are used to generate the ch 3-4 output. It has signal return
    blocking diodes to prevent leakage back to the antenna built into the
    switching circuit.

    Dtv converters on the other hand are very sophisticated digital electronic
    packages and no doubt the possibility of this working is a figure of about
    a billion to the negative since very few digital decoding circuits have
    encoding functionality. I will not totally rule out the possibility of an
    IC that does both but it would not be cheap enough to go into these cheap
    converters.

    So until someone can provide actual proof of models that work this way and
    it is reproducable by anyone I'll put this one on the shelf with the old
    fashoned snake oil ads and cold fusion.



    Gnack
     
  13. Probability equals exactly .000000000000000000000000....

    The encoding process is far more complex than the decoding process so one
    can be sure that it won't be there by accident.

    And even if it was present in the circuitry, hooking electronics up
    backwards rarely does anything useful - this assuming it doesn't actually
    smoke. :)

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