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Creating a Colpitts Oscillator

  1. Feb 7, 2012 #1
    I am creating an experiment to show how wireless energy can be transferred through resonantly tuned lc circuits. In order for this to work i need an oscillator. I have been told to try a colpitts oscillator. I have looked online and found a few sites showing calculators and schematics for these oscillators but I am having trouble in a few places.

    http://how-to.wikia.com/wiki/How_to_build_an_oscillator_circuit

    and

    http://www.ekswai.com/en_cap3.htm

    show the diagram but dont show where the positive and negative terminals are for the dc power into the oscillator and where the output is. Where are these things?? On the wiki page it has a diagram for a 50 MHz oscillator and I am probably looking for only a few MHz.
     
  2. jcsd
  3. Feb 7, 2012 #2

    vk6kro

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    Science Advisor

    In those diagrams, Vcc is the positive connection and the "ground" symbol (like a triangle) is the negative connection.

    I wouldn't suggest a Colpitts oscillator. They are relatively hard to get going because you have to get the ratio of some capacitors right.

    You could look for crystal oscillator modules around 4 MHz. These are often used on discarded boards form old computers or you can probably get one for a few dollars.

    You just connect 5 volts to them and take the signal out of one of the pins. Easy.

    There are some here:
    http://www.futurlec.com/cgi-bin/search/search.cgi?search=crystal_oscillator&search_base=10&page_no=2
    That 4.9152 MHz one would be suitable.
    You need to choose one where you can listen to it in a receiver.
     
  4. Feb 8, 2012 #3
    Ok thanks. But I would like to if i can get more than 5 volts out of the system. Do crystals allow you to do that?
     
  5. Feb 8, 2012 #4

    vk6kro

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    Science Advisor

    Crystals do, but these crystal oscillators do not. They are strictly 5 volts out. Colpitts oscillators using transistors are usually much weaker than this.

    However 5 volts from an oscillator is a very good start and it is relatively easy to amplify from 5 volts to get a greater voltage. At least you start on a known stable frequency.

    I should issue the usual warning about unwanted radiation.
    Unless you have a licence to transmit on these frequencies, it is illegal in most countries to do so.
    Low powered, short range experiments are normally OK as long as they are not heard outside your own property. You should check on the regulations in your area.

    You may be surprised at how strong the signal from one of these oscillator modules can be, especially in the same room.
     
  6. Feb 8, 2012 #5
    Ok thanks!! I will try the crystal oscillator then. Thanks for all the help.
     
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