FM Transmitter

What is FM transmitter circuit

The FM transmitter circuit (Frequency modulation) is a circuit made up of a single transistor or a BJT. In a wireless communication, the (frequency modulation) FM carries the data or information by changing the frequency of the carrier wave as per the information or a message signal.

The Fm transmitter achieves the application of (very high frequency) VHF radio frequencies of 87.5 HZ to 108 MHZ in both transmission as well as receiving the FM Signal. The FM Transmitter completes the most excellent volume with in less power.

The performance and working of the FM transmitter circuit is dependent upon the variable capacitor and inductor. In the article, you are going to learn that how you can prepare a FM transmitter circuit and how does it work with its various applications.

What is FM Transmitter?

The FM transmitter is a circuit that uses a very low power to operate and does uses (Frequency Modulation) FM Waves to transmit the sound. With the help of such FM transmitters we can easily transmit the audio signals with through the carrier waves with different frequency.

The frequency of the carrier wave would be the same as for the audio signal with an amplitude. The FM Transmitter produces a range of VHF from 88 HZ to 108 MHZ.

Block Diagram for FM transmitter circuit

Components required for FM transmitter circuit are modulator, oscillator, RF-Amplifier, Audio pre-amplifier, microphone and antenna. The Diagram shows the Block diagram for FM transmitter circuit. There are two types of frequency signals in the signal :

  • Carrier signal (with carrier frequency)
  • Audio signal (With audio frequency)
FM transmitter circuit Block diagram
FM transmitter circuit Block diagram

The carrier frequency is obtained by modulating the audio signals. The (Frequency Modulation) FM signal is obtained by differentiating the carrier frequency and by allowing the Audio frequency. The transistor is used for oscillator purpose in order to obtain Radio Frequency signal.

Working of simple FM Transmitter Circuit explanation

The circuit diagram shown for FM transmitter circuit and the electronic components are the resistor, capacitor, trimmer or variable capacitor, inductor (coil), transmitter, mic, 9v of power supply or 7809 Voltage regulator (in case if you are using input voltage more than 9v) and an antenna. The mic or a microphone is assumed to grab the sound signals and there is a presence of sensor with capacitance value inside the mic. The change in pressure of air or AC signal causes in production of such capacitance.

FM Transmitter Circuit diagram
Simple FM Transmitter Circuit Diagram

The Oscillation circuit could be made with the help of Transistor 2N3904, Inductor and the variable capacitor. The Transistor 2N3904 used in FM Transmitter Circuit. It is a NPN transistor which is basically used for signal and voltage amplification purposes. If the current is passed through L1 Inductor and the variable capacitor, the FM Transmitter Circuit will start oscillating with the resonant to that of the carrier frequency (I.e frequency of the carrier signal).

The negative current or the negative feedback will result C2 Capacitor to the Transmitter Circuit. The oscillator is required in FM Transmitter Circuit in order to generate the radio frequency carrier waves. The transmitter circuit is capable of storing the energy for the oscillation as it is a derived from the (inductor and capacitor) LC circuits. The audio I.e input signal obtained from the mic is passed through the base of the transistor in order to modulate the output signal of the LC circuit in FM (I.e frequency modulation wave) Form.

Here, the main purpose of the variable capacitor becomes that to vary the resonant frequency in order to obtain the best FM Signal Frequency band. The modulated signal is then transmit or radiated as a radio wave with the frequency of FM frequency range. The antenna is nothing but a piece of good conductor, in our application we’d used a copper wire of 30cm long and 26 gauges thick. You can use copper wire up to 25-27 inches long as an antenna in the circuit, the length of the antenna however must be significant.

Application of FM Transmitter Circuit

  • FM Transmitter Circuit are used in a sound system as a signal transmitter.
  • These are used in wireless components used in vehicles and offices.
  • The circuits are used to make FM transmitters used to reduce the noise in certain places.

Advantages of FM Transmitter Circuit

  • The FM Transmitter Circuit could be made very easily as the very common components are used which are very cheap and easily available.
  • Above circuit gives the very high efficiency to the in transmitting signal in a shorter range.
  • The circuit is best suited for demonstration and fm transmitter circuit project.
  • The circuit does have a large and complicated components.
  • The transmitter circuit is capable to neglect the noise signal through the amplitude variation.

Disadvantages of FM Transmitter Circuit

  • In above FM Transmitter Circuit, there is a large wider channel needed.
  • With the Circuit, the transmitter as well as the receiver tends to become more difficult.
  • The received signal gets poor quality as there an interference occurs in the medium.
  • The above circuit is not good enough for high power fm transmitter circuit purpose.

After making the FM Transmitter Circuit you will be able to understand the basic working and application of the transmitter. Hope the article helped you. Feel free to share about how do you like or your queries in a comment below.

You may want to see Arduino and Bluetooth moduleDistance measurement with arduino and ultrasonic sensor.


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