Project report
Abstract
This report is on the design and working of the FM receiver .This report splits into two portions FM
receiver and its power amplifier .The job of the FM receiver is to demodulate the frequency signal
while power amplifier is used to amplified the result
Introduction:
The FM radio receiver project report. The fm band transmission has started very recently in india but
its superior technique and quality has attracted the listener .Unlike Am, the Fm is seprate band and its
frequency ranges from 88MHz to 108MHz.The FM band cannot be received by conventional FM
receiver. Each and every AM receiver does not incorporate FM facility. The present project is very low
cost project and it can be adjusted to any radio receiver system to receive fm transmission.
Antenna:
A theoretical study of radiation from a linear antenna(length l)
Power radiated a (p/I)
2
This implies that for sane antenna length, the power radiated by short wavelength and higher frequency
Would be large .Hence the power effected by long wavelength base band signal would be small for good
transmission.
Modulation.
In amplitude modulated communication ,propagation of radio waves from the transmitting antenna
to receiving antenna take place in following two ways.
1. Ground wave propagation
2. Sky wave propagation
The transmitted radio waves are supported at their lower edge by the ground.The radio waves
have to be vertically polarized ,so as to prevent the short circuiting of electric field component
of the wave. The radio waves induces current in the ground. over which it passes
Types of modulation
Amplitude Modulation:
In the frequency range 500KHz to 30MHz amplitude modulation of the signal is employedand
accordingly this frequency range is termed as amplitude band (AM band).The earths atmosphere is
more or less transparent to the electromagnetic waves in AM band. However the ionosphere does not
allow the electromagnetic waves in AM bands to penetrate it and they are reflected back. When the
frequency of electromagnetic waves is above 40Hz, they are no longer reflected by the ionosphere but
Project report
undergo refraction. Keeping the above facts in mind the amplitude signal in medium wave frequency
range (up to 1500KHz) is transmitted by surface wave propagation or also called Ground wave
propagation. In the short wave frequency range (from a new MHz to 30MHz) the amplitude modulated
signal is transmitted via reflection from the ionosphere .It is also called Sky wave propagation.
.It is also called Sky wave propagation.
Frequency Modulation:
For frequency of elctomagnetic waves above 40MHZ, frequency modulation of the signal is preferred.
In transmission of TV signal ,the frequencies of electromagnetic waves employed ranges from 30MHz to
1000MHz .The transmission of electromagnetic waves in this frequency range can never range be made
by surface wave propagation nor by sky wave propagation .The surface propagation is not possible for
the reason that the ionosphere cannot reflect the electromagnetic waves in this frequency range .
Circuit Diagram.
Project report
Components Required:
S.N0 component Qty
1 BF494 2
2 capacitor(22pF) 1
3 capacitor(0.22F) 1
4 capacitor(0.1F) 1
5 capacitor(220F) 1
6 resistor(22k) 1
7 IC LM386 1
8 audio out 1
9 battery 1
Working.
The circuit works off a small 4.5 volt battery or two 3.6 volt Lithium button cells.
The fm receiver section has two RF transistors T1 and T2 to detect the Frequency Modulated signals.
Coil L1 and the trimmer capacitor form the tuned tank circuit to tune the receiver to the best FM station
with strong signals. The signals are capacitor coupled through C2.
10K preset VR controls the volume to the input of the amplifier. IC1 is the micro power audio amplifier
that works between 4.5 to 12 volts DC. The amplified sound can be heard through the low impedance
head phone or small Mylar speakers.
FM radio coil
Coil is the important part of the FM tuner. It is made up of 18 SWG enameled copper wire. Wind 4 turns
on a ball pen to get 0.5 cm inner diameter. Remove the enamel from the tip of the wire and solder
tightly in the PCB. Trimmer and coil should be soldered very closely. Adjust the spacing of the coil
winding if necessary to get the station clearly. Assemble all the receiver components as close as possible
to get better result.
