FM Transmitter

[Shakeel]

Hi
please tell me what is the function of capacitor along the collecter emmiter terminals in the F M Transmitter.

I am attaching the circuit along with mark capacitor.

[Guest Kasamiko]

It's a feedback capacitor connected across emitter and collector of the transistor to sustain the RF oscillation.. ;D

rhonn ;) ;)

[steven]

:)i posted a circuit like that in one of the forums for a big ear circuit that transmitts what it hears, to your fm radio and when tuned it picks up everything nice and clear. it may be in the circuits reqest section under parabolic microphone circuit reqest

[Guest Yevgenip]

It's a feedback capacitor connected across emitter and collector of the transistor to sustain the RF oscillation..

That is a very cool sentence my friend 8)

[Kevin Weddle]

That capacitor is an emitter element that has an impedance somewhere around the value of the emitter resistor. The only reason that it is not grounded is because it allows the inverted output to be fed back reducing the high gain capability presented by the tank circuit. The impedance of a resonant circuit is interesting. Remember that polar diagram where you have XC 180 degrees from the XL. You always subtract to find the net affect. This is for the series circuit. In the parallel circuit, one value is going to dictate over the other. The lower impedance will decide whether the circuit appears inductive or capacitive. Now, at the resonant frequency, the impedance is the same and neither dictates the impedance. Just as much energy that is released by the capacitor is absorbed by the inductor and the circuit will not absorb more energy. Hence a high impedance.