FM RADIO TRANSMITTERPrepared by : Bhavin K. Vekariya B.Sc.(IC)

Shree M. & N. Virani science college

Reaccredited at the level “A” (CGPA = 3.28) by NAAC, “STAR college Department status” by MST-DBT 

A “College with Potential for Excellence-CPE (phase –||) by UGCAccredited at the level G-AAA “A-1”

Level by KCG Government of Gujarat.Rajkot 360 005

ABSTRACTThe aim of the project is to aware and develop a knowledge of

simple FM-Transmitter to be used specialized application such as in radio broadcasting and telecommunication etc.

Frequency modulation(FM) has several advantages over the system of Amplitude modulation(AM) used in alternate form of radio broadcasting.

The most important of these advantages is that system has greater freedom from interference and static.

This circuit of FM transmitter is simple and it has a range of 100 m to 2 Km.

Commercial FM radio station are assigned frequencies between 88 to 108 MHz and will be the intended frequency range of transmission.

INTRODUCTION FM radio transmitter is the transmitter that transmit the radio

audio signal on carrier wave by Frequency Modulation. A FM transmitter is a low power FM radio transmitter that

broadcast a signal from portable device to a standard FM radio. This transmitters is broadcast the signal over an FM broadcast

band frequency, so that it can be picked up by any nearby radio. This allows portable device to make use of louder and better

sound quality for various application in everyday life without required a wired connection.

Being low-powered, this transmitters typically have a short range of 30 – 2000 meters depending on the quality of the antenna, receiver, obstructions and elevation.

PRINCIPLEFM transmission is done by the process of audio pre

amplification, then the audio wave is modulated, now the modulated signals(waves) transmitted by the antenna after that the transmitted signals is received by the receiver(radio) and demodulated and after that we can hear the audio. These signal are in the range of 88 to 108 MHz.

WHAT IS MODULATION & DEMODULATIONMODULATION: The process of changing some characteristics

(e.g. amplitude, frequency or phase.) of the carrier wave in accordance with the intensity of the signal is known as Modulation. There are three basic types of modulation, ⟹namely (1) Amplitude Modulation (2) Frequency Modulation (3) Phase Modulation. Here we are discussing only ⟹Frequency Modulation (FM). When the frequency of the ⟹carrier wave is changed in accordance with the intensity of the signal then, it is called Frequency Modulation(FM).

DEMODULATION: The process of recovering audio signal from the modulated wave is known as Demodulation.

Process of Modulation

PARTS LISTRESISTORR1 – 10KR2 – 15KR3, R4 – 4K7R5 – 2K2R7 – 22ER8 – 1KR9 – 10E

CAPACITORC1 – 2.2/25VC2, C10, C5, C11, C6 –

1Kpf (102), 001KpfC3, C8 – 01Kpf (103)

10KpfC9 – 15pf

SEMICONDUCTORSQ1 – BC 548 BelQ2, Q3 – C 2570

TRM 1,2,3 – 2........22pfMIC – 2 Pin Cond. MikeL1 – 7 Turn 22 Swg

L2 – 6 Turn 22 SwgL3 – 5 Turn 22 SwgL4 – 5 Turn 22 SwgBattery – 9VAntenna – 70cm Antenna

OR WIREPCB

Circuit diagram

CIRCUIT OPERATION⟹FM transmission is done by the process of audio pre

amplification. First we amplifying the audio signal, generating ⟹a carrier signal using an oscillating and then modulating the carrier signal with the amplified audio signal. Audio input from ⟹microphone is first amplified using the common emitter configuration of transistor. The amplified signal is then given ⟹to the oscillator circuit through the coupling capacitor. The ⟹oscillator circuit generates a signal with a frequency determined by the value of variable capacitor. The output signal from the ⟹emitter of the transistor is coupled to the input of the power amplifier transistor using the coupling capacitor. As in the ⟹power amplifier section tends to maintain an output matching with that of the oscillator. The amplified RF signal is then ⟹transmitted using antenna.

USES AND APPLICATIONFM transmitters are commonly used to broadcast a stationary

audio source. It also used as simple cordless mike at educational institution. It can be used fro commercial and non-commercial

broadcasting. It is also used for in homes for parental control and care of their

babies. In private securities services and in fieldwork for

communication purpose. It can be also used for spying purpose. Also it is useful as a simple cordless mike.

ADVANTAGESThis Circuit is small and can be easily used.this circuit easily constructed at low price.It has noiseless reception.Operating range is quit large. it is less affected by buildings and can received indoors.The efficiency of transmission is very high.Waves at higher frequencies can carry more data than the

waves at low frequency.Smaller geographical interference between neighbouring

station.

DISADVANTAGESThe biggest problem with FM transmitter is the

potential for outside interference. Outside interference may occur with nearby radio channels like pagers, walkie-talkies.

Some time device drift from their targeted frequencies.This system also not a secure system.Receiver are required for the everyone.It requires at least one free channel between the

channels to prevent the interference.

“I discovered an Invisible Empire of the Air, Intangible, yet Solid as Granite”

- Lee De Forest (Father of Radio)

Thank You

“Find the Laws of the Nature, Understand them and Use them”