Understanding an FM transmitter circuit

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SUMMARY

The discussion focuses on the operation of an FM transmitter circuit, specifically the role of components in the right half of the circuit. The circuit utilizes a Colpitts oscillator configuration, where L2 and C5 form the tank circuit responsible for generating the carrier frequency. C6 functions as a feedback capacitor to maintain oscillation, while C3 and R5 create a low pass filter to allow human voice frequencies to be modulated and transmitted. The circuit's design effectively demonstrates the principles of frequency modulation using these specific components.

PREREQUISITES
  • Understanding of Colpitts oscillator design
  • Familiarity with tank circuits and their components
  • Knowledge of low pass filter functionality
  • Basic electronics principles, including capacitors and inductors
NEXT STEPS
  • Study the operation of Colpitts oscillators in detail
  • Learn about tank circuit calculations for frequency modulation
  • Explore low pass filter design and its applications in audio transmission
  • Investigate the role of feedback capacitors in oscillator circuits
USEFUL FOR

Electronics students, hobbyists building FM transmitters, and engineers interested in radio frequency design and modulation techniques.

nickerst
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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!
 
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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?
 
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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