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Transistor as FM modulator

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baby_1

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Hello friends
i want to design a FM Transmitter with transistor.i see a lot of circuit that use transistor az modulator.but in university we didn't read anything about transistor az fm modulator. i want a good reference that explained Transistor az FM modulator and tell more about it (theory and experimental)

Thanks a lot
 

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Thanks dear itzvinodh

but i want know about transistor as modulator theory and experimental things(how it modulate two signal in FM transmitter) where should we inject the signals? and other things like these.
 

To modulate the frequency of an oscillator, varactor diode is preferred. Transistors do not have the desired variable-capacitance response. Some transistors can be found but using a diode is much simpler and the results are better. A transistor is often used as amplitude modulator, but in high-frequency (>10 MHz) range, a PIN diode is again better and offers more predictable results than a transistor.

You can find more details in good textbooks.
 

Thanks jiripolivka
but as you see this url
**broken link removed**
you will know that most of the frequency modulator use transistor az modulator instead of PIN or Varactor diode
 

Actually the right way to say (using your words) is: "most of the CHEAP AND FOUND ON THE NET frequency modulator use transistor az modulator instead of PIN or Varactor diode".

As was stated, a good frequency modulator would use varactors, and do not modulate the internal capacitance of the transistors, which are hardly affected by the transistor bias, resulting a poor FM modulation with a lot of AM components.
 

Thanks vfone
i read some refrences and know you are right.
could you tell me a book or application note about baias transistor and the theory of fm modulation with it?
 

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