28-01-2013, 02:46 PM
Frequency Modulation (FM)
1Frequency Modulation.pdf (Size: 1.88 MB / Downloads: 38)
INTRODUCTION
In telecommunication, frequency modulation (FM) conveys information over a
carrier wave by varying its frequency. FM is commonly used at VHF radio
frequencies for high-fidelity broadcast for music and speech. Usually 87.5 – 108.0
MHz is used to transmit and receive the FM signals. Designing and assembling of
the FM transmitter is difficult task.
Designing of PCB
Designing of PCB is made by a special software name “EXPRESS PCB”. It is the
best software to make the circuit Schematic and the circuit layout. We should have
knowledge to operate this software. In this software there is a number of option for
making the circuit layout. Firstly we takes one by one component and then draw
the layout as shown in the figure.
Drilling:
Drilling is used after the getting the circuit layout printed on the pcb. On
the component place we require holes which is drilled by hand drill machine which
is normally available.
Soldering:
It is the final step on the circuit. In this step we mount component on the
PCB with the help of soldering Iron.
CAPACITOR:-
A capacitor or condenser is a passive electronic component
consisting of a pair of conductors separated by a dielectric (insulator). When a
potential difference (voltage) exists across the conductors, an electric field is
present in the dielectric. This field stores energy and produces a mechanical force
between the conductors. The effect is greatest when there is a narrow separation
between large areas of conductor; hence capacitor conductors are often called
plates.
Capacitors are widely used in electronic circuits to block the flow of direct current
while allowing alternating current to pass, to filter out interference, to smooth the
output of power supplies, and for many other purposes. They are used in resonant
circuits in radio frequency equipment to select particular frequencies from a signal
with many frequencies.
Inductor Coil
Inductance (measured in henry) is an effect which results from the
magnetic field that forms around a current carrying conductor. Current flowing
through the inductor creates a magnetic field which has an associated
electromotive field which opposes the applied voltage. This counter electromotive
force is generated which opposes the change in voltage applied to the inductor and
current in the inductor resists the change but does rise. This is known as inductive
reactance. It is opposite in phase to capacitive reactance. Inductance can be
increased by looping the conductor into a coil which creates a larger magnetic
field.
An inductor is usually constructed as a coil of conducting material, typically
copper wire, wrapped around a core either of air or of ferrous material. Core
materials with a higher permeability than air confine the magnetic field closely to
the inductor, thereby increasing the inductance. Inductors come in many shapes.
Most are constructed as enamel coated wire wrapped around a ferrite bobbin with
wire exposed on the outside, while some enclose the wire completely in ferrite and
are called "shielded".
Antenna
A plastic wire or telescopic aerial can be used as the antenna. The
length of antenna is very important to send the suitable range. As the rule the
length of the antenna should be ¼ of the FM wavelength. To determine the length
of antenna, use the following equation.
Condenser MIC:
It is a transducer which is used to pick up the sound signals. It
converts sound signal into the electrical signal. It is easy in soldering. It’s small
structure make it very useful component in the electronics field. The diaphragm
inside the MIC vibrates according to the air pressure changes and generates
electrical output signal. Variable resistor is used to adjust the current through the
MIC. It requires low power.
APPLICATION
This circuit is mainly used for the transmitting audio signal like music, voice into
the VHF band. So everyone in the range of the transmitter can hear voice or music
in their FM receiver like radio. It is only the basis of the project work. With the
help of this project we can show how the sound signals are transmitted in the VHF
band via the FM transmitter. This is the best example of the FM modulation & it
shows project work on the Communication field.