TV transmitter?

Discussion in 'Wireless & RF Design' started by Mathematics!, Jan 21, 2010.

  1. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    For this TV transmitter in a previous post
    http://forum.allaboutcircuits.com/attachment.php?attachmentid=15395&d=1263845213

    For the video in what is the format of the video in suppose to be.
    It looks like you are modulation a carrier in the VHF channel using AM modulation for the video signal.

    If this is the case I am trying to figure out what colors corospond to what when modulating this carrier using AM?
    Basically forget the audio I only want the video portion of this circuit but for the video input I want to plug it into the second VGA port of my computer. I know VGA I can look up the pin out but I don't know how the video in signal has to be converted to for the transmitter to broadcast the video from my computer ?

    Thanks for any help
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Does the video-card have a composit video out?
    Then the circuit will do.
    Otherwise the VGA signal has to be converted to composit video.
    This is not so easy as the scanrates will mosttimes differ from the broadcast video.

    Greetings,
    Bertus
     
  3. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
    1,022
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    Ok , my graphics card has VGA , DVI , and s-video that is it.
    If you are refering to composite RCA red,white,yellow then NO.

    But I think I can make a VGA to RCA cord or at least buy one.
    Another way is converting the VGA (RGB color schematic to Y, U and V for the composite video )
    Their are formulas you can use to do this maybe I can convert it to thru software and then send it out the VGA port in someway.

    Either way I am curious what the amplitude has to be to make it a green color pixel , or a red , or a black ,....etc on the TV. Is it like the max amplitude is the brightest , and the min amplitude is the darkest (black).... just duno when modulating this carrier what amplitude corosponds to what color????

    Thanks for any help
     
  4. bertus

    Administrator

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  5. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    Wait I have S-video connector on the graphic card isn't this doing the same format as RCA composite so I could use this? Yes/No?
    And I am in Massuacheutts , USA (new england area) by boston , new york , vermont ,...etc
    It's either one of NTSC, PAL, and SECAM duno which one yet.
     
  6. bertus

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  7. Wendy

    Moderator

    Mar 24, 2008
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    It used to be NTSC, but now it is other. Most video devices still have NTSC in the USA.
     
  8. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    well, I am trying to go from my computer to an OLD CRT TV.
    probably in the 1995ish area.

    What I am curious of is the TV demodulation circuit for this TV.
    The TV only has RCA YRW plug's and a coaxial plug for a coaxial cable or antenna.

    If I put the computer graphic card in just black and white would their be any difference in usings S-video or RCA composite I read that they are both analog

    S-video pin out is
    1 - S-Video Luminance Ground 2 - S-Video Chrominance Ground 3 - S-Video Luminance Signal 4 - S-Video Chrominance Signal
    In the mean time I will looking into your links.

    Tell me if you think this should have any problems
    I am also think for testing this circuit first to use my DVD player for broadcasting to the TV. My DVD player has the composite RCA out and I can then run the output of the RCA plugs on it to the TV transmitters video in.

    Just read part of this
    http://www.tkk.fi/Misc/Electronics/circuits/svideo2cvideo.html
    If that is all I have to do use a 470pf cap then wow that is pretty easy and I am going to do it this way.
    Thanks for that
     
  9. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    Also curious if I make this what type of wire should I use and how long can I make it 5 ft , 10 , 50ft ,...what is the exceptable range?
    It would be nice if I can use 22gage wire and make it about 30ft or so.

    Thanks again
     
  10. bertus

    Administrator

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  11. Mathematics!

    Thread Starter Senior Member

    Jul 21, 2008
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    yes , but it doesn't look like RCA composite , S-video , or VGA cables ,...etc use coaxial cable?

    Maybe they do under their black outer covering duno?
    Either way if coaxial is the cable I have to use then I need to use 4 them this seems cumborsome.....
     
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