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Simple FM Transmitter carrier wave

Discussion in 'General Electronics Discussion' started by Ricardo7890, Dec 10, 2012.

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  1. Ricardo7890

    Ricardo7890

    6
    0
    Jul 17, 2012
    There's something i don't understand about this circuit.From what i hear the reactive elements to the right produce the carrier wave, which is in FM frequencies, which is modulated by the microphone, which carries the sound.What i don't understand is how those waves are made, from what i see i can't make out how they would create an oscillating current. They should be able to create an oscillating current independently of the microphone, but i don't understand how, could someone please explain. bug-sch.gif
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    There is a tuned circuit formed from the inductance and two capacitors in series. The transistor gets an input via its emitter at low impedance and outputs the same current at high impedance. There is therefore a power gain which is used to maintain oscillation.

    VHF oscillators are often difficult to understand because the transistor inductances and capacitances often play a crucial part. Here the change of transistor capacitance with voltage provides the modulation.

    Note that the antenna is coupled tightly to this circuit and so will affect the frequency
     
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