I was looking for a project to make for fun when i found this FM transmitter, i got curious because it is a best project for fun as well as you tube, it is a simple FM transmitter but i make it it the simplest. I replaced the variable capacitor with a fixed one, re-calculated its frequency to be able to tune it only by the coil instead of the variable capacitor.
This circuit design is unstable because its resonant frequency drifts off if you get your hands close to the antenna or the circuit, the length of the antenna affects the resonant frequency so you should fix it on a fix place so that its frequency remain constant.
Note: It is a very simple transmitter but its range can be 2 km if u attach long antenna with it.
- R1 : 100ohm resistor
- R2 : 4.7 ohms resistor
- C1 : 1nF ceramic capacitor
- C2 : 47pf ceramic capacitor
- Q : bc2655,2n222 or 2N3094
- L : 212nH (5 turns of 15 gauge copper wire)
- Mic : Condenser mic
- Bat : 3v battery and its holder
- Ant : Ideally a piece of wire, 1/4 or 1/2 of the wavelength of the frequency if you want more range then use roof antenna and adjust frequency to increase and decrease the space between inducter coil.
6v battery can be used to increase the range of this transmitter
Working of FM Transmitter Circuit
The following circuit diagram shows the FM transmitter circuit and the required electronic and electrical components for this circuit is the power supply of 3v to 6V, capacitor,resistor, induct-or, mic and antenna. Let us consider the microphone to understand the sound signals and inside the mic there is a presence of captive sensor. It produces according to the vibration to the change of air pressure and the AC signal.
FM transmitter circuit requires an oscillator To generate the radio frequency carrier waves. The tank circuit is derived from the LC circuit to store the energy for oscillations. The input audio signal from the mic penetrated to the base of the transistor, which modulates the LC tank circuit carrier frequency in FM format. The variable capacitor can be used to change the resonant frequency for fine modification to the FM frequency band but i did not used variable capacitor because i have to made it very simple for students. The modulated signal from the antenna is radiated as radio waves at the FM frequency band and the antenna is nothing but copper wire of 20 cm long and 24 gauge. In this circuit the length of the antenna should be significant and here you can use the 25-27 inches long copper wire of the antenna or you can also increase its length with inductor coil for adjustment.
Application of Fm Transmitter
- The FM transmitters are used in the homes like sound systems in halls to fill the sound with the audio source.
- These are also used in the cars and fitness centers.
- The correctional facilities have used in the FM transmitters to reduce the prison noise in common areas.
- It can also be used as hidden security voice.
Advantages of the FM Transmitters
- The FM transmitters are easy to use and the price is very low with clear sound.
- The efficiency of the transmitter is very high.
- It has a large operating range.
- This transmitter will reject the noise signal from an amplitude variation so it has very clear sound.
Disadvantages of the FM Transmitter
- In the FM transmitter the huge wider channel is required.
- The FM transmitter and receiver will tend to be more complex.
- Due to some interference there is poor quality in the received signals
In this article we have discussed about the FM transmitter circuit working and its applications. I hope by reading this article you have gained some basic knowledge about the working of FM transmitter.
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