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The FM (Frequency modulation) transmitter is an electronic circuit that manipulates a carrier signal wave to transmit useful information or data. Also, it uses a single transmitter and does not require a massive power supply to transmit audio input signals over long or short distances. For an FM transmitter circuit to work, you need a portable audio device like an MP3 player or mobile phone.

How to Make an FM Transmitter Circuit

FM transmitter Circuit Production Tools

Here are the things you need to make an FM transmitter circuit:

9v Battery

Variable capacitor

Antenna

Microphone or any other audio input

Inductor

Resistors and capacitors

Transistors

Circuit Diagram and Description

If you’re new to this, circuit diagrams might look a bit confusing. But, don’t worry, we are here to make things simple. Take a look at this practical diagram of a circuit. This circuit diagram shows an FM transmitter with a 9v power supply. Plus, the mic is the input device that receives the sound signals.

Hence, you can generate sound radio waves signals when you speak into the mic. Also, the microphone has capacitive plates that create energy from the sounds you make. Then, it varies the audio wave at the divider junction and turns it into audio signals. After this, the capacitor (C1) cancels out the noise from the audio signal and sends it to the transistor (Q1).

The transistors send the sound signals to the LC tank circuit. Plus, the circuit is necessary because it generates the motion of fixed frequency. The audio signal coming from the transistor will then modulate the signal of fixed frequency. Then, the modified signal transmits to the antenna, which sends the sound signal to any receiver within 30 meters.

FM Transmitter Circuit Design

The FM transmitter circuit has various designs ranging from simple to complicated. So, let’s look at two basic techniques that are common and easy to create.

Wireless Design

The wireless circuit design sends signals that transmit over a radio tuned to the matching frequency band. The frequency depends on how the inductor gets placed and the values of C1, C2, and C3. Plus, you can manipulate the coil turn distance or diameter to make the perfect response over FM receivers.

A small wire antenna (about 3 inches) may be attached at the shown point to make the bug highly responsive and create distortion-free signals. So, here’s the design of the wireless FM transmitter circuit.

One Transistor Design

This design is the most straightforward transmitter circuit to make. However, its simplicity creates some certain drawbacks like:

Small transmitting range

It operates a 1.5v battery with limited capabilities The one transistor design doesn’t use a microphone as its sound input device. Instead, its antenna serves a dual function (it detects and transmits sound vibrations). Also, it doesn’t have a frequency-determining stage. Thus, it cannot be called a tuned transmitter circuit.

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