FM Radio Receiver
FM Ratio Receiver Project Report. The FM Band transmission has started very
recently in India but its superior technique and quality has attracted the
listeners. Unlike AM, the FM is a separate band and its frequency ranges
from 88MHz to 108 MHz. The FM Band can not be received by the conventional
AM receivers. Each and every AM receiver does not incorporate FM facility.
The present project is a very low cost project and it can be fitted to any
radio receiver/audio system to receive FM transmission. The circuit of this
project is very simple and can be easily assembled.
A theoretical study of radiation from a
linear antenna (length l)
This implies that for the same antenna
length, the power radiated by short wavelength or high frequency signal
would be large. Hence the effective power radiated by long wavelength base
band signal would be small for a good transmission, we need high power
hence, this also point out to be need of using high frequency transmission.
In amplitude modulated communication,
propagation of radio waves from the transmitting antenna to the receiving
antenna takes place in the following two important 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 the electric field
component of the wave. The radio wave induces current in the ground, over
which it passes. It attenuates to some extent due to partial energy
absorption by the ground.
Types of modulations
In the frequency range 500 kHz. to 30 MHz,
amplitude modulation of the signal is employed and accordingly this
frequency range is termed as amplitude modulated band (AM bond). The earth’s
atmosphere is more or less transparent to the electromagnetic waves in AM
band. However, the ionosphere (the topmost layer of the atmosphere) does not
allow the electromagnetic waves in AM band to penetrate it and they are
reflected back. When the frequency of electromagnetic waves is above 40 MHz,
they are no longer reflected by the ionosphere but undergo refraction.
Keeping the above facts in view, the amplitude modulated signal in medium
wave frequency range (up to 1500 kHz.) is transmitted by surface wave
propagation or also called ground wave propagation. In the short wave
frequency range (from a few MHz to 30 MHz), the amplitude modulated signal
is transmitted via reflection from the ionosphere. It is called sky wave
For frequencies of electromagnetic waves
above 40 MHz, frequency modulation of the signal is preferred. In the
transmission of TV signals, the frequencies of the electromagnetic waves
waves employed ranges from 30 MHz to 1000 MHz. The transmission of
electromagnetic waves in this frequency range can neither be made by surface
wave propagation nor by sky wave propagation. The surface wave propagation
is not possible for the reason that the ionosphere cannot reflect the
electromagnetic waves in this frequency range. Further, in the frequency
range 30 cm. to 10 m. FM transmission are made from small antennas.
Now-a-days there is a necessity of FM
projects in the electronic market. Through this project different FM
stations can be tuned but in India. Presently there is one FM channel. As
such the project is designed for one channel to avoid possible damage of the
coil in tuning again and again. The FM transmission is stereo phonic. As
such you can connect it to any stereo deck and enjoy the stereo sound. Now a
days two-in-one and radios with FM band are available in the market. But
without replacing your old radio set you can connect this project to your
old radio/two-in-one and enjoy the FM transmission. It is quite economical
too. Unlike AM receivers, the FM receiver is assembled through different
(i) FM Amplifier
(v) Discriminator (Detector)
(vi) Audio Pre-Amplifier.
All the functions are performed by the IC-5591 which is
employed in the circuit. The audio signal available from the preamplifier is
fed to audio output amplifier for further amplification. The RF of FM band
transmission is fed to pin no. 2 of the IC TA5591 through the aerial, which
also works for FM amplifier, oscillator and mixer stage. A ceramic filter of
10.7 MHz. is connected to the local oscillator pin no. 4, 5 and 6 of IC. A 9
volt DC supply is fed to pin no. 8 of the IC. Pin no. 10 of the IC is
discriminator pin. The audio signal is available from pin no. 11 of the IC.
Pin no. 18, 19 and 20 of the IC are IF amplifier pins while pin no. 22 and
24 are local oscillator pin. Two trimmers are connected to the circuit. The
range of the frequency can be varied by rotating the trimmers. A gang
condenser equivalent to the value of the trimmer can also be used in place
of trimmer if available. This project can operate in the range of 3V to 12
Volt DC supply. However the trimmers are to be adjusted to get best
Ceramic Filter 10 MHz.
Resistance 56 E
Capacitor 470 PF
Capacitor 22 PF
4.7 MFD/63 V.
One Pole two way switch