FM TRANSMITTER
AIM: To design and study working of FM Transmitter.
APPARATUS: Q1- Transistor- 2N3904
Capacitors- 4.7pF, 20pF, 0.001uF, 22nF.
Variable capacitor
Resistors-4.7 kilo Ohm, 470 Ohm
Antenna
Condensor/ Electret Microphone
Inductor- 0.1uF or 6-7 turns using 26 SWG wire
INTRODUCTION: A FM transmitter is a low power FM radio transmitter, which
allows listening music or any other audio message from CD player, portable
media player or any other audio system which is used to be played by a nearby
FM radio. Because of low cost of the equipment’s for an FM transmitter, leads
to rapid growth in the year of world war II. After the 3 years from the war,
600 licensed FM station were broadcasting in the US and, by the end of 1980
there were more than 4,000 stations. Due to crowding in AM broadcast and
failure of basic AM receiver to remove noise. FM transmission helped us to
overcome from these detriments and therefore, can be used to transmit music,
or audio signals and this may leads to rising the number of auditors to famous
as well as classical music, by which FM station draw the higher audience
ratings as compared to AM stations. FM transmitter consist of mice from
where an audio signal is transmitted to different section of transmitter, after
processing the signal from these section it will transmit through antenna and
these signal catch by receiver side antenna.
CIRCUIT DIAGRAM:
WORKING OF FM TRANSMITTER:
The following circuit diagram shows the FM transmitter circuit and the required
electrical and electronic components for this circuit is the power supply of 9V,
resistor, capacitor, trimmer capacitor, inductor, mic, transmitter, and antenna. Let us
consider the microphone to understand the sound signals and inside the mic there is
a presence of capacitive sensor. It produces according to the vibration to the change
of air pressure and the AC signal.
The formation of the oscillating tank circuit can be done through the transistor of
2N3904 by using the inductor and variable capacitor. The transistor used in
this circuit is an NPN transistor used for general purpose amplification. If the
current is passed at the inductor L1 and variable capacitor then the tank circuit
will oscillate at the resonant carrier frequency of the FM modulation. The
negative feedback will be the capacitor C2 to the oscillating tank circuit.
To generate the radio frequency carrier waves the FM transmitter circuit requires an
oscillator. 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 is used to change the resonant frequency for
fine modification to the FM frequency band. 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 20cm 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 circuit.
ADVANTAGES OF FM TRANSMITTER:
• The FM transmitters are easy to use and the price is low
• 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.
WAVEFORMS:
APPLICATIONS:
Radio broadcasting
Two way mobile radio
Microwave communication
TV sound transmission
Cellular radio communication
Satellite communication.
RESULT:
Design of FM transmitter was done and its working was studied
