What is a High Range FM Transmitter?

An FM Transmitter is an electronic device that can air audio signals from a source on a selected range of frequencies. They are generally used to broadcast stationary audio from devices such as TV & computers, around a room. They are inexpensive & simple to design. So, in today's article, we will look into a step-by-step tutorial on how to make a High Range FM Transmitter circuit using some NPN transistors & a small no. of other components.

Whatever may be the schematic scope or design, every FM transmitter is based on the same three key stages: Audio pre-amplification, Modulation and, transmission. The first stage generally consists of amplifying & filtering an input audio signal. In the second stage, the input audio signal is modulated and a carrier signal is generated by a variable frequency oscillator circuit. In the last stage, the modulated audio signal is transmitted using an antenna between the FM frequency range of 88MHz to 108MHz.

FM Transmitter PCB
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Hardware Components

You will need the following parts to build this project.

S.NoComponentValueQty
1)FM Transmitter PCB-1
1)NPN Transistor2N39042
2)Condenser mic5mm1
3)Variable Capacitor40pF1
4)Inductor0.1uH1
5)Capacitor0.1uF, 0.01uF, 4.7pF3
6)Enameled copper wire18 AWG1.5ft
7)Resistor1M, 100K, 10K, 1K, 100 Ohm7
8)Soldering Iron45W - 65W1
9)Soldering Wire with Flux-1
10)DC Battery9V1
11)Battery Clips-1
12)Jumper Wires-As per need

Circuit Diagram

Working Explanation

The working of this circuit is pretty simple, an input audio signal from a device such as a smartphone is taken through an electret mic. Here, a coupling capacitor of 0.1uF is used to block the DC component of the signal, allowing only AC to flow. This signal acts as a control signal to the base of the 2n3904 transistor (Q1).