Guide to Building FM transmitter

 If you've ever been fascinated by radio waves and the art of transmitting your own signals, then building your very own FM transmitter is an exciting and rewarding project to undertake. With a DIY FM transmitter, you can explore the realm of wireless communication and broadcast your own audio content over the airwaves. Whether you're a hobbyist looking to delve into the world of radio technology or simply want to experiment with transmitting signals, this guide will provide you with the fundamental knowledge and step-by-step instructions to create your own FM transmitter from scratch. 

We have already shown different FM transmitter circuit that you can build at home. Here it is explained the building blocks of a typical simple FM transmitter so that one can also modify, improve an FM transmitter circuit or any wireless communication circuits. 

The following shows a simple FM transmitter circuit diagram.

FM transmitter circuit

The above FM circuit consist of following blocks.

a. Power Supply

b. Audio Input Circuit

c. Audio Pre-Amplifier

d. Oscillator and Modulator circuit

e. Antenna

a. The power supply circuit consist of 9V battery, a power supply smoothing capacitor to reduce power supply noise and a switch.

b. The audio input circuit consist of and electret microphone, pull up resistor R1 and coupling capacitor C2. See Wireless FM Microphone Circuit for more.

c. The audio microphone pre-amplifier circuit is made up of BJT transistor 2N3565 which is biased with the resistors R2, R3 and R4.

d. The oscillator and modulator circuit is made up of the transistor 2N5179 BJT transistor, air coil inductor L1, capacitors C1 and C6, biasing resistors R5, R6 and R7. The BJT transistor along with the inductors L1, capacitors C1 and C6 makes up the Colpitts oscillator. The coil size can be calculated using the online air core inductor calculator at the FM frequency band. The inductance required for the oscillator can be calculated using the online oscillator calculator.

C3 is a coupling capacitor that couples the amplified audio signal from the pre-amplifier into the oscillator and modulator circuit. The capacitor C5 is used to couple the high frequency oscillatory signal to the ground and thus preventing the high frequency component going into the amplifier circuit. 

The FM modulator is a reactance modulator. The audio signal changes the transistor junction capacitances which in turns are added and subtracted from to the oscillator tank capacitances(C1,C6) that then changes the frequency of oscillation of the FM wave. 

The resulting FM signal is then ac coupled to the antenna via the coupling capacitor C7.

Once you know what blocks are essential to build an FM transmitter circuit, you have choices to use another different type of oscillators, modulator, audio input circuit, battery and antenna.

For example you can use crystal oscillator, Colpitts oscillator, Hartley oscillator, FET Pierce oscillator etc. You can use different type of FM modulator like varactor FM modulator circuit.

 So, grab your soldering iron, gather your components, and let's embark on this electrifying journey of building your very own FM transmitter!

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