EE-304 COMMUNICATION SYSTEMS
PROJECT REPORT
Section-C
Submitted by:
MOHAMMAD WASTI 17-EE-165
SAUD REHMAN 17-EE-176
ABDUL WAHAB 17-EE-102
Department of Electrical Engineering
HITEC University Taxila
Submitted To:
Engr. Talha Asghar
TABLE OF CONTENTS
1. Objective
2. Apparatus for transmitter
3. Apparatus for receiver
4. Circuit diagrams
5. Working of FM Transmitter
6. Applications of Transmitter
7. Advantages and Disadvantages of FM transmitter
8. Working of FM Receiver
9. Applications of FM Receiver
10. Advantages and Disadvantages of FM Receiver
11. Conclusion
FM TRANSMITTER AND RECEIVER
OBJECTIVE:
IMPLEMENTATION OF THE AM TRANMITTER AND RECEIVER.
APPARATUS:
TRANSMITTER:
Resistors (4.7k,470ohm)
Capacitors(4.7pF,20pF.0.001uF,22nF)
Variable capacitor/ Trimmer capacitor (0-100pF)
Inductor(0.1uF/6-7 turns using 26 SWG wire)
Transistor(2N3904)
Antenna(15 cm wire)
Mic(microphone)
Battery(9 V)
Connecting wires
RECEIVER:
Resistors(10k,1k)
2 Transistors(494)
Capacitors(100uF,100nF,220nF,2.2nF)
Variable capacitor/ Trimmer (30pF)
Antenna (15cm wire)
Inductor(6-8 turn 5mm diameter)
Battery(9V)
Connecting wires
Vol controller (22k pot)
CIRCUIT DIAGRAM:
FM transmitter:
FM RECEIVER:
Working:
AM TRANSMITTER
FM transmitter is the whole unit, which takes the audio signal as an input and delivers FM wave
to the antenna as an output to be transmitted. The block diagram of FM transmitter is shown in
the following figure.
The working of FM transmitter can be explained as follows.
The audio signal from the output of the microphone is sent to the pre-amplifier, which
boosts the level of the modulating signal.
This signal is then passed to high pass filter, which acts as a pre-emphasis network to
filter out the noise and improve the signal to noise ratio.
This signal is further passed to the FM modulator circuit.
The oscillator circuit generates a high frequency carrier, which is sent to the modulator
along with the modulating signal.
Several stages of frequency multiplier are used to increase the operating frequency. Even
then, the power of the signal is not enough to transmit. Hence, a RF power amplifier is
used at the end to increase the power of the modulated signal. This FM modulated output
is finally passed to the antenna to be transmitted.
Application of Fm Transmitter
The FM transmitters are used in the homes like sound systems in halls to fill the sound with
the audio source.
These are also used in the cars and fitness centers.
The correctional facilities have used in the FM transmitters to reduce the prison noise in
common areas.
Advantages of the FM Transmitters
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.
Disadvantages of the FM Transmitter
In the FM transmitter the huge wider channel is required.
The FM transmitter and receiver will tend to be more complex.
Due to some interference there is poor quality in the received signals
FM Receiver
The super heterodyne receiver takes the amplitude modulated wave as an input and
produces the original audio signal as an output. Selectivity is the ability of selecting a
particular signal, while rejecting the others. Sensitivity is the capacity of detecting RF
signal and demodulating it, while at the lowest power level.
Radio amateurs are the initial radio receivers. However, they have drawbacks such as
poor sensitivity and selectivity. To overcome these drawbacks, super
heterodyne receiver was invented.
RF Tuner Section:
The amplitude modulated wave received by the antenna is first passed to the tuner
circuit through a transformer. The tuner circuit is nothing but a LC circuit, which is also
called as resonant or tank circuit. It selects the frequency, desired by the AM receiver.
It also tunes the local oscillator and the RF filter at the same time.
RF Mixer:
The signal from the tuner output is sent to the RF-IF converter, which acts as a mixer. It
has a local oscillator, which produces a constant frequency. The mixing process is done
here, having the received signal as one input and the local oscillator frequency as the
other input. The resultant output is a mixture of two
frequencies [(f1+f2),(f1−f2)][(f1+f2),(f1−f2)] produced by the mixer, which is called as
the Intermediate Frequency (IF).
The production of IF helps in the demodulation of any station signal having any carrier
frequency. Hence, all signals are translated to a fixed carrier frequency for adequate
selectivity.
IF Filter:
Intermediate frequency filter is a band pass filter, which passes the desired frequency. It
eliminates all other unwanted frequency components present in it. This is the advantage
of IF filter, which allows only IF frequency.
We know that in FM modulation, the amplitude of FM wave remains constant. However,
if some noise is added with FM wave in the channel, due to that the amplitude of FM
wave may vary. Thus, with the help of amplitude limiter we can maintain the amplitude
of FM wave as constant by removing the unwanted peaks of the noise signal.
In FM transmitter, we have seen the pre-emphasis network (High pass filter), which is
present before FM modulator. This is used to improve the SNR of high frequency audio
signal. The reverse process of pre-emphasis is known as de-emphasis. Thus, in this FM
receiver, the de-emphasis network (Low pass filter) is included after FM demodulator.
This signal is passed to the audio amplifier to increase the power level. Finally, we get
the original sound signal from the loudspeaker.
Application of Fm Receiver
widely used for FM radio broadcasting.
It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures
via EEG
ideal for two-way radio communication or mobile communication application.
Advantages of FM Receiver
It is resilient to noise and interference.
It is also easier to apply modulation at a low level power stage of a transmitter.
With the help of frequency modulated signals, we can use RF amplifiers.
Disadvantages of FM Receiver
FM doesn’t have as efficient spectral efficiency as some of the other modulation formats.
Frequency modulation has a little more complicated and slightly more expensive
demodulator than the AM.
The sidebands for frequency modulation transmission extend out to infinity. While they
are significant for wideband FM transmissions, they fall small for narrow band FM.
Filters are used.
CONCLUSION:
FM transmitter depends on an oscillator that produces carrier signal on a particular frequency.
When the particular signal needs to be controlled, then a voltage modulator is used.
The FM signal is then transmitted into the outer space through an antenna.
An FM receiver is a superheterodyne type like a typical AM receiver. For FM receivers, this
IF is 10.7 MHz. The intermediate frequency wave is amplified using IF amplifier and then its
amplitude is maintained constant using a limiter.
