Trouble shooting circuit

Discussion in 'Wireless & RF Design' started by nerdegutta, Oct 31, 2010.

  1. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    785
    Hi,

    I've tried to make a tv/video transmitter circuit, short range. So I googled around and found a circuit, and modified it a bit/removed the audio part.

    See thread:

    http://forum.allaboutcircuits.com/showthread.php?t=33002

    So now I have this, see attached files.

    Problem is... It doesn't work. So far, I found that it's frequency is about 3.1-4.0 MHz. I just don't get it. Guess you guys see the problem in the schematic right away.

    In the three open holes, I've put the pot.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    are u sure u don't have solder bridges?
     
  3. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    I'm quite sure I don't have solder bridges. That's one of the first things I check.

    But I cannot be to sure enough, I'll check again....
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Try pulling the inductor apart a bit more and post how much the frequency changes.

    Adjusting it's value/length may get enough change in. If it doesn't change much, then something else is wrong.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The traces are quite long for the intended frequency.
    Are you really using a BC547 as transistor?
    That is a universal transistor and not a real RF transistor like the BF199 or equal types.

    Bertus
     
  6. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Yes, I'm using the BC547. Maybe I should change to another. What do you suggest, I don't think I have the BF199.

    So you think the traces are too long... Hmm... Thought I put the components close together.

    Is the schematic OK?
     
  7. bertus

    Administrator

    Apr 5, 2008
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  8. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Thank you.

    I will try to build the one in post #3, changing the NPN's to something similar I got.

    Anyway. The schematic I postet, shouldn't it work. In theory?
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In theory it should work.
    I only have some doubts about the used transistor.

    Bertus
     
  10. nerdegutta

    Thread Starter Moderator

    Dec 15, 2009
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    Just got mail from my local dealer. (Maybe supplier is a better word... :))

    I will buy a couple of:

    2N2907A
    BF199

    I saw the long list of transistors in another tread, so I sent him the list. All he had was these... Anyway, looking forward to some quality time at the lab.... :D

    Thanks.
     
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