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getting FM mofulation using varactor diode

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New Member
Hi everyone, :D
what i know about the varactor diode is that it changes its capactance according to the applied voltage across it (when connected in reverse biase with the source),therefor ,it can be used in a tank circuit which is a part of FM circuit....correct me if iam wrong.
the tank circuit(which has the varactor part of it) needs a DC voltage to ring .at the same time the varactor diode needs an AC voltage to change its capactance and the frequency of the tank circuit(varactor in parallel with inductor).
using that we can get an oscillation signal keep changing its frequency according to to the AC input signal(forget about the continuity of oscillaton).what ineed to know is the connection of both supplies(DC/AC) to the tank circuit to get FM oscillation.(iwill be thankful if some one has a small circuit with explations)


Active Member
I am sorry that I don't have the ability to post diagrams however you can find what you need in various ARRL (American Radio Relay League, ham radio) handbooks.

It is my understanding that the varactor (or other) diode can be placed in parallel with the other capacitor(s) in an oscillator circuit - and that the varying voltage (such as that from a microphone) will modulate the frequency. The amount of shift or deviation is dependent on the circuit and of course, the diode. With this little bit of information you might simply look for information on various RF oscillators - knowing that the diode is in parallel with the capacitor in the tank circuit.
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