# How An Fm Transmitter Works?

1. May 14, 2012

### fizikzede1

I am a beginner at circuit design.i need to find a way to explain how an fm transmitter works which i do not
so any of you my sincere friends can explain to me how the circuit below works and does the necessary calculations i'm in your debt

Here is sample proteus file and circuit diagram :

#### Attached Files:

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• ###### FmTransmitter11.zip
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Last edited: May 14, 2012
2. May 14, 2012

### sophiecentaur

Sorry
I can't see either of the files you posted.

3. May 14, 2012

### skeptic2

4. May 14, 2012

### vk6kro

You are probably interested in how the signal gets frequency modulated.

Somewhere in the transmitter there is an oscillator whose frequency depends on the resonant frequency of a tuned circuit.
A frequency modulator varies either the inductance or the capacitance of this tuned circuit.

A common method is to use a variable capacitance diode whose capacitance varies with the voltage put on it.
This can be a specially designed diode, or it can be a power rectifier diode, or even a LED. But the diode is always reverse biased.
It also needs to be a poor rectifier at the frequency in use or it will generate unwanted DC voltages in the circuit.

So, as the audio produces a variable voltage on the diode, the frequency of the transmitter is also varied.

There are simple FM transmitters which operate at VHF where the variable capacitance is not obvious, but it is achieved by varying the voltages on the transistor in the oscillator and this varies the capacitance of the device. This may be the circuit you intended to attach.

5. May 14, 2012

### fizikzede1

Thanks a lot :) I updated circuit diagram and proteus file you can see at attachment.

6. May 20, 2012

### bs061096

yaa, the whole circuits works with a certain frequency which is based on the LC ciecuit or tank circuit.

7. May 20, 2012