Transistor as modulator

Thread Starter


Joined Jun 3, 2011
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 aa FM or AM modulator. i want a good reference that explained Transistor az modulator and tell more about it (theory and experimental)
it because of i read some where that transistor should be in nonlinear mode not linear mode for modulation... i need more and compelete reference

Thanks a lot


Joined Dec 28, 2011

You may want to search for VCO which uses varactor to control the carrier frequency. You can add a buffer at the output of the VCO to prevent loading by the antenna.

Hope it helps!


Joined Dec 20, 2007
There are hundreds of FM broadcast band transmitter circuits on the internet and a few AM broadcast band transmitters. Look at them in Google.

They are modulated by having the modulation change the current which changes the voltage in the oscillator transistor. The FM transmitter oscillator's frequency is changed because its capacitance changes when its voltage changes.

The AM oscillator's changing current creates AM.

The transistor oscillators are linear.