DESIGN AND CONSTRUCTION OF PORTABLE FM TRANSMITTER
An FM transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves. Frequency modulation (FM) transmitter generates the radio waves by varying the radio signal’s frequency slightly. FM transmitter is basically a VHF colipits oscillator capable of transmitting sound or music to any standard FM receiver. The circuit works on a D.C source which makes it for a pure rectification. FM transmitter also has a capacitor microphone which picks up very weak sound signals. This FM transmitter was designed using transistors and other component such resistor, inductor and capacitors. This project transmits frequency on 100MHz± 5%.
The transmitting distance is l00metres. It is powered with 9volts D.C battery using suitable F.M receiver tuned to the transmitting frequency of this project. F.M Transmitter can be used as cordless microphones, mobile phone and for public address purposes. The distant of transmission is limited to 100m and fixed frequency of transmission, away from all other radio station. This gives best range and least interference. The antenna is attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, and garage door openers. In more powerful transmitters, the antenna may be located on top of a building or on a separate tower, and connected to the transmitter by a feed line, that is a transmission line.
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1.1 BACKGROUND OF THE STUDY
Information transmission is very vital to human life just as the early men used sticks to produce sound which indicates the location of each other as they wander about also down to the middle era when town crises come into play for the same information propagation to be transmitted from one point to another with the aid of radio communication which necessities the application of radio transmitter and receiver.
Frequency modulation (FM) is a technique for wireless transmission of information where the frequency of a high frequency carrier is changed in proportion to message signal which contains the information (Chen, 2002). FM was invented and developed by Edwin Armstrong in the 1920’s and 30’s. Frequency modulation was demonstrated to the Federal Communications Commission (FCC) for the first time in 1940, and the first commercial FM radio station began broadcasting in 1945 (Mohn, 2007).
In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant.In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music is broadcast over FM radio.However, the concept of FM is essential to a wide gamut of radio frequency wireless devices and is therefore worth studying (“The Future of Radio”, 2008).
1.2 STATEMENT OF THE PROBLEM
The comparatively low cost of equipment for an FM broadcasting station, resulted in rapid growth in the years following World War II. Because of overcrowding in the AM broadcast band and the inability of standard AM receivers to eliminate noise, the tonal fidelity of standard stations is purposely limited. FM does not have these drawbacks and therefore can be used to transmit music, reproducing the original performance with a degree of fidelity that cannot be reached on AM bands. FM stereophonic broadcasting has drawn increasing numbers of listeners to popular as well as classical music, so that commercial FM stations draw higher audience ratings than AM stations. The integrated chip has also played its part in the wide proliferation of FM receivers, as circuits got smaller it became easier to make a modular electronic device called the “Walkman”, which enables the portability of a tape player and an AM/FM radio receiver. This has resulted in the portability of a miniature FM receiver, which is carried by most people when travelling on long trips. Listeners are most interested in easily being able to select radio stations to have better sound quality and audibility and to increase accessibility for people with visual and auditory impairments. Listeners also want a wider range of radio channels over the whole country. Consumers’ needs must be met hence the need for advancements in the field of radio broadcast. This project work will explain the process of designing and constructing of an FM transmitter (“The Future of Radio”, 2008).
1.3 OBJECTIVE OF THE STUDY
The objective of this project is:
1. To review some modern digital technologies that has been developed for effective FM signal generation.
2. To show the design and components of a FM transmitter
3. To show the construction process of an electronically operated system known as FM transmitter capable of transmitting a frequency modulated signal.
1.4 SCOPE OF THE STUDY
This project work covers the design and construction of FM transmitters for quality audio transmission and explains some of the modern trends in FM signal generation, highlighting their prospects. It also covers the advantages these technologies offer over traditional radio broadcasting and brings to light various distinguishing features possessed by these technologies.