Understanding an FM transmitter circuit

  • Thread starter nickerst
  • Start date
  • #1
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200M-FM-transmitter-circuit.png


Homework Statement .

I am just trying to understand this cicuit a little better. Especially the right half, I know that the left half is just acting as an amplifier but I'm not sure how the right half works. Also how is the frequency being modulated here?


The attempt at a solution.

I know that C5 and L2 are used to calculate the carrier frequency, but I am very unfamiliar with this type of set up for Q2. Any help would be greatly appreciated!
 

Answers and Replies

  • #2
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What I've gathered so far is that L2 and C5 are acting as an oscillator to modulate the frequency at a steady sine wave. C6 appears to me to be just a capacitor to keep it oscillating. Does this all sound correct so far?
 
  • #3
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This is a colpitts oscillator, with L2 and C5 comprising the tank circuit. C6 is the feedback capacitor which produces the modulated signal. C8 is a decoupling capacitor attempting to maintain the voltage across the circuit. C3 and R5 make up a low pass filter, passing frequencies equal to that of human voice through to be modulated and transmitted. And R6 is just the emitter current limiter. Is this correct? If anyone has any idea at all to the correctness of this post please feel free to reply. Thank you!
 

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