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FM Transmitter
An Independent Project
Instructor:-Dr. Kiran Kuchi
Indian Institute of Technology
Hyderabad
 Our Model……….
Introduction
The audio of audio devices is converted to FM radio signals by
means of FM Transmitter and then these frequency modulated
signals are picked by FM Receivers(radios) and audio can be
then played on reciever.FM Transmitter is connected to audio
output of audio devices.
Circuit Diagram
Components used
Part
Total Qty.
Description
C1
1
0.001uf Disc Capacitor
C2
1
5.6pf Disc Capacitor
C3,C4
2
10uf Electrolytic Capacitor
C5
1
3-18pf Adjustable Cap
R1
1
270 Ohm 1/8W Resistor
R2,R5,R6
3
4.7k 1/8W Resistor
R3
1
10k 1/8W Resistor
R4
1
100k 1/8W Resistor
Q1, Q2
2
2N2222A NPN Transistor
L1, L2
2
5 Turn Air Core Coil
MIC
1
Electret Microphone
MISC
1
9V Battery Snap, PC Board,
Wire For Antenna
.
Working Principle
 Transmitted signal is Frequency Modulated (FM) which means
that the carrier’s amplitude stays constant and its frequency
varies according to the amplitude variations of the audio signal.
 The circuit involves three stages (2 RF stages and one audio
preamplifier for the modulation).
 The first stage is pre-amplification stage
 The second(RF) stage is an oscillator.
 The last (RF) stage is a tuned amplifier that boosts signals from
the oscillator
 Use of the additional RF amplifier increases the range of the
transmitter.
Pros & Cons
Pros
 Audio signal can be broadcasted on any FM frequency from 87.5
to 108.0 MHz by this transmitter.
 An FM transmitter can be made to plug into the headphone
jack or output port of a portable audio or video device, such as a
CD player, portable media player, or satellite radio system. The
sound is then broadcast through the transmitter, and plays through
an FM broadcast band frequency.
Pros & Cons
Cont.…
Cons
 But….most devices on the market typically have a short range of
up to 100 feet (30 metres) with any average radio (up to about 300
feet (100 metres) with a very good radio under perfect conditions) .
 The output power of FM Transmitters is very low so when it comes
to use in areas where large number of other radio signals are
present. It becomes unsuitable because strong FM signals can
bleed over into neighbouring frequencies making the frequencies
unusable with the transmitter.
Thank You
Submitted by: Gaurang Rokad
 Shashank Jaiswal