Single transistor to amp crystal oscillator

Discussion in 'Wireless & RF Design' started by Synaps3, Jun 5, 2013.

  1. Synaps3

    Thread Starter Member

    Jun 5, 2013
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    So I got a 2N2222 transistor and hooked up the base to the output of the crystal oscillator, the emitter to the ground, and the collector to the antenna along with some extra voltage from a 9V battery. It makes the signal worse. Do you know what I am doing wrong? I am not even sure if you can just use a single transistor and no other circuits to amplify an RF signal. Is this possible?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    You cannot simply connect a transistor to an antenna and expect to get an effective RF transmitter. You need a tuned LC circuit matched to the antenna.
     
  3. Synaps3

    Thread Starter Member

    Jun 5, 2013
    67
    2
    So if I just added an LC circuit, it would work? I looked it up and it looks like I need an inductor and a capacitor. If it is as simple as adding an LC circuit and it will work, then how do I calculate what inductor and capacitor I need?

    I am trying to build a transmitter as simply as possible with the least components. When I look online I can only find complex circuits that I am sure with some extra time, I could build, but I wouldn't have a clue what I was doing and how all the components work.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    What is the frequency of your crystal oscillator and what distance do you want to transmit?
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    The transistor needs to be configured as an amplifier, with input bias,coupling/matching circuits, and a load.
     
  6. Synaps3

    Thread Starter Member

    Jun 5, 2013
    67
    2
    Are you saying I would need more than just an LC circuit as MrChips suggested?

    The frequency is 1Mhz. I am not really interested in a specific distance, I'd like to just get it to go father than about 30 feet (which is how far it goes with no amplification).
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    The LC circuit in conjunction with the antenna will form the output load for the amplifier. You still need to design a biasing circuit to establish the Quiescent point of the amplifier in the absence of a signal and connection of the emitter to ground will limit your ability to "amplify" an AC waveform.

    For example if you choose a linear (Class A) Common Emitter configuration you will need an emitter bypass circuit consisting of a parallel RC from emitter to GND.

    If you choose a Class C circuit then the biasing circuit will have to be designed for a different Q-point.

    I think you have some investigation to do.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    1) Are you aware that there are regulations and restrictions governing the transmission of radio frequency signals?

    2) Did you know that you need a license in order to operate a transmitter of a certain frequency and radiated power?

    3) Are you aware that 1MHz falls in the commercial AM/MW band and can be disruptive to licensed commercial services?

    Transmitting RF energy is a form of EMI and RF pollution. We don't think of it this way but imagine if one were to operate a 1000W sound system or 1000W light bulb in one's backyard, audible and visible for the whole neighborhood to experience. RF pollution is the same except we don't hear or see it.

    If you are going to experiment with transmitting an RF signal, check what frequency and radiated power is allowed for unlicensed operation.
     
  9. Synaps3

    Thread Starter Member

    Jun 5, 2013
    67
    2
    That's just to be sure I'm not wasting any power when there's no amplitude, right? Or is it necessary?

    What should the emitter be connected to? So I have the base connected to the signal to amplify, the collector connected to an LC circuit which is then connected to the antenna along with extra voltage. Then where do I put the ground?

    Thanks for answering my noobish questions. I appreciate it!


    Yes
    Yes
    Yes

    I know the laws in my area and I have access to an oscilloscope to make sure I am not breaking any.
     
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