Design and Construction of an FM Wireless Microphone
CHAPTER ONE
AIM AND OBJECTIVE OF INVESTIGATION
my aim and purpose to investigation started when I saw that thing\s are not easy in the field as it is said theoretically. When I bought components and made connections in a project board, I saw that my objectives were not attained immediately I disconnected several times and moved to the library, consulted our senior course mate for further explanation and serious investigation. In fact my purpose is not as easy as thought to us. Then I added more effort to am at the final level of the project.
CHAPTER TWO
TRANSMITTER
The transmitter amplifiers, transforms and combines electrical signals to form suitable for propagation. Since at signals are seldom enough to be transmitted through the space, a modulated R.F. signal is amplified to increase the power and is fed to the aerial of the transmitter.
The signal passes though series of amplification necessary for propagation. The simplest aerial radiate with more or less equal strength in all directions. Like other forms of electrometric radiation radio wave can be reflected at a suitable surface. Some transmitter have a reflector made of sheeth of a metal or a wire mesh to consecrate the beam of radiation form the transmitter in a covering direction. These are often used in transmitter in telecommunication network. When the information is not intended for the public and when a transmitter of a relatively low power is being used to send message over a long distance. They are also used in transmitting to and from satellites dishes for similar reasons. It has been stated that electromagnetic wave travels in straight line but due to the spherical nature of the surface of the earths devotion from transmitter cannot be received directly at prints beyond the horizon.
IONOSPHERIC PROPAGATION
Ultra – violet radiation from the sun entering the atmosphere of the earth supplies energy to the gas molecules of the atmosphere. This energy is sufficient to produce Ionization of the molecules, that is, remove some electrons from their parent atoms. Each atom losing an electron in this way has a resultant positive change and is said to be ionized.
Ionosphere is a set of layers of the earth’s atmosphere which reflect radio wave and cause them to flow the earths contour. High frequency waves are reflected back towards the ground and can be received for away and beyond the horizon. Within the ionospheric layer the electron density increase with the increase in height above the earth.
In the ionosphere, layers exist within which the free electron density is greater than the heights immediately above or below the layer. Four layers exist in the daytime, the 8,E,F1, & F2 layers.
At night-time the ultra-violet radiation ceases, no further free electron are produced, and the D layer disappears because of the high rate of recombination at the lower attitudes. At 100km or so above the earth, the recombination rate is much less and the E layer, although becoming weaker does not normally disappear. During the hour of F1 and F2 layers merge to form a single F whose height varies consideration.
CHAPTER THREE
FREQUENCY MODULATION
F.M (frequency modulation) arose from the search for something better than amplitude modulation. It is a system of modulation in which the amplitude of the modulating carrier is made constant, whereas its frequency is varied in accordance with the amplitude of the modulating signal. Frequency modulation is used on the V.H.F band and has several advantages. For frequency modulation, observe that.
– The amplitude of the carrier remains unchanged
– The period becomes smaller for high amplitude of the modulating signal and widens for reduced amplitude of modulating signal.
CHAPTER FOUR
THE RADIO TUNER
A radio tuner is a radio receiver minus audio amplifier. It therefore performs all the functions of the radio receiver in selecting (tuning} amplifying and demodulating a signal, except. That it does not amplify the audio signal from the detector to a point where it is capable of driving a loudspeaker. Since a hi – fi system has its own and 10 amplifiers, this latter function, obviously is not required. To qualify as a hi – fi component, a radio tuner (am or fm) must incorporate special high – quality design features. Most important, the rf, if, and detector circuits of the tuner must pass the entire audio modulation band impressed on the carrier despite this large bandwidth, the tuner must be sufficiently selective to separate two closely spaced stations, to prevent any interference between them. The sensitivity of a tuner should be in the order of a few microvolts to pull in weak signal.
CHAPTER FIVE
FM WIRELESS MICROPHONE (FM TRANSMITTER
Frequency modulation (FM) transmitter is also known as FM wireless microphone.
Definition: frequency modulation (fm) transmitter is a device that transmits audio signal (message, music etc. (at a particular frequency band it transmits through an electromagnetic wave. It operates at frequency band of 108.1MHZ and over a distance of 16 meter. Circumference. Suitable low value this may be achieved by separation, screening or balancing out by means of signal fed from the transmitter. The acho signal received by the receiver will now be a weaker signal of the same type of fm as that rate retreated by delayed by a time corresponding to the two may path to the reflecting object.
CHAPTER SIX
CONCLUSION
The invention of f.m. transmitter has in no small measure helped in the growth of technology and economic improvement of this nation and of the whole world. The frequency modulation transmitter or fm wireless microphone, transmits signal from the microphone to receivers in a cited frequency band.
When signals or message are into the microphone an alternating e.m.f. is generated. An alternating current flows through the resistor connected in series with the microphone.
Amplification occurs when the inductor sends an induced e.m.f to the transistor and modulation take place as a result of the carrier signal being passed through the modulator circuit. If a radio wave is to convey a message, some feature of the wave must be varied in accordance with the information to be transmitted. Modulation helps to check interference and noise and this enable the message to be sent out and heard or received vividly.
The signals after being modulated is sent out to A.F preamplifier for the amplification of the audio signals.
This amplified signal are sent to the radio frequency amplifier for proper amplification of the radio frequency.
It is in the R.F amplifier in the block diagrams in he figure that helps in smoothening and filtering of the signals place. The amplified r.f. signal is than fed to the aerial of the transmitter. The simplest aerial radicate with more or equal strength in all directions. The radiates from the aerial are sen through electromagnetic induction wave to listening with stereo reproducing facilities, who receives and enjoys good stereo reception.
Like other forms of electro-magnetic radiation, radio-waves can be reflected at a suitable surface. It has been stated that electromagnetic radiation travels in straight lines. The radiation electric and magnetic field are at right angles, and both are at right angles to the direction of propagation.
The surface of the earth is not that so hard, that radiation from a transmitter cannot be received directly at points beyond the horizon. Fortunately there is a natural reflector, which allows us to receive radio transmission at greater distance.
REFERENCES
- G.N Patchett: Radio Servicing Volume 2 Electronic Devices and A.M Receivers (c) Norman Price (Publishers) LTD. 1956 Fifth Edition, 1977.
- J.A Betts: Signal Processing, Modulation and Noise Copyright (c) 1970. Holder and Stoughton Educational, A Division of Holder and Stoughton
- James Eke: Basic Elements of Physical Electronics Copyright (c) 2003 by James Eke.
- R.F.W. Coates: Modern Communication System 1975. The Macmillan Press Limited London and Braking Stroke Associated Companies in New York, Bublin, Melbourne, Johannesburg and Madras.
- Bradford L: Smith and Michel Hensi Carpenter Microwave Engineering Handbook Vol. 1 The University Press, Cambridge Great Britain.
