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27mhz transmitter design

Discussion in 'General Electronics Discussion' started by Makedonianin, Feb 20, 2010.

  1. Makedonianin

    Makedonianin

    3
    0
    Feb 20, 2010
    Hi, I'm in a need of a 27Mhz transmitter design input (20hz-15khz).
    Now I'm kinda lost in all the literature i have.
    In my uderstanding I need an amplifier and modulator, so basically 2 transistors.
    Also maybe someone experienced could tell me which modulation would be better for use AM,FM and why?
    Any help appreciated :)
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    There are surely loads of designs out there on the web. What are you trying to achieve here? And what about the power level? Building a plasma speaker?
    You seem to only want the tx, but why the 20Hz-15kHz spec. and then no preference for modulation, when the receiver will be the specifying/ limiting part?
     
  3. Makedonianin

    Makedonianin

    3
    0
    Feb 20, 2010
    Hi,
    Thanks for such a quick answer ;)
    Well this my university project. I had a little to do with the requirements ( carrier 27mhz, 10mW, input 20-15khz). So i have a lot of freedom in design.
    I'm basically building a simple wireless guitar system. And I don't want to take a already done circuit, soldering isn't my point here :D I want to do it myself, just need some hint,pointers in the right direction :)
     
  4. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Ok, so your hands are not tied in any way and you don't need to consider the receiver, but;
    27MHz is prone to "skip", interference & noise (but not worse that it's been used for remote control models etc.). The wavelength is also quite long which is a challenge for an efficient antenna design. Also, a 15Khz bandwidth being over 4 times the usual bandwidth is making it non-compliant with regulations.
    Apart from those issues FM is the natural choice for noise-free reception, as AM would be prone to clicks & buzzes from mains switches etc.
    You can build a simple oscillator with varicap diodes as the modulating elements. Then follow this with an output stage. You might get away with a 3-transistor device.
    But I'd rather try to use a 4046 CMOS PLL as the modulating element, with a crystal-controlled frequency for stability. A frequency multiplier will certainly be neccessary between this and the output stage. I'm not able to help you with the RF design in itself though, that's kind of a black magic even to me.
     
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