Short range TV Transmitter

Discussion in 'Wireless & RF Design' started by nerdegutta, Jan 18, 2010.

  1. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi,

    I'm looking for a small, short range TV transmitter. So far I've found this circuit.

    But I need only transfer the video, not the audio. Can I skip the parts on the left side of the red line?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Seems reasonable to me. Don't leave C3 off though.
     
  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Yes, you are right.
    The circuit round Q1 is the audio modulator.
    As Bill said do not forget to mount C3.

    Greetings,
    Bertus
     
  4. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Thank you.

    So it would be more like this?
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Yes, C3 is needed for decoupling the powersupply.

    Greetings,
    Bertus
     
  6. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Thanks.

    I appreciate your time and effort.

    Beside studying company economics, this will be my upcoming weekend project.

    :)
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Does it also say someting about the coil in the oscillator?
    With the current transistors a VHF channel can be used, most preferable channel 2 to 4.
    If you want to go on higher channels other transistors should be used.

    Greetings,
    Bertus
     
  8. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi,

    it's says that it's transmitting somewhere around 50 - 210MHz in the VHF band.
     
  9. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi,

    I found the same circuit on another site. There it said that L1 should be 4 turns, 6mm core turn with 24 swg.
     
  10. bertus

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    Apr 5, 2008
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  11. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi,

    Thank you for the link. I've read the page once before, and I will read it again.

    :)
     
  12. knowitall

    New Member

    Jan 10, 2010
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    You will go nuts trying to keep the Osc. stable, especialy if breadboard.
    My advice is to use an old rf mdulator from a throw away V.C.R.
    There not hard to spot, or to wire up, old video games , pong ect. would also use such a device, output is selectable on CH. 2 or 3.
     
  13. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi.

    I thought I would breadboard it, and check the frequency with my frequency counter. A DVM13MC2 bought from www.jameco.com and check.

    I have a buch of crystals laying in my drawer, can I somehow hook it up to make the Oscillation more stable?

    Thanks for the answer.
     
  14. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Breadboarding a RF circuit is not so good idea.
    The stray capacities will give a lot of trouble.

    A while ago I posted a link to the "manhatten style prototyping"
    http://forum.allaboutcircuits.com/sh...9&postcount=30

    This hold a kind of inbetween the breadboard and the dead bug.
    Becouse the wiring can be shorter as in the dead bug style, it is fine for RF.

    Greetings,
    Bertus
     
  15. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Hi, Bertus.

    Yes I remember that post. Read the page a few times. I think I will take the time to draw and etch a PCB for this, since the oscillation is so important.

    Is it possible to use a crystal to make the oscillation more stable?
     
  16. bertus

    Administrator

    Apr 5, 2008
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  17. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Thanks.

    Now I have a lot of reading to do. (Lucky me, I can print the web page to a PDF file, transfer it to my Kindle, and read it in bed, just before i watch NCIS :))

    Is there any equivalent transistor for the BFR91?
     
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