Design and construction of an fm transmitter using phase- locked loop for public announcement system

Abstract

Dissemination of information is the basis of all communication around the globe and a backbone for societal development. In the era of technology, radio frequency (RF) application has become eminent in information transmission. Inevitable there would be Public address system due to inherent limitation in human voice. A public address (PA system) is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a given sound. This project elucidates simple design and cost-effective digital transmitter-receiver to replace emerging traditional PA system which apparently has shortcomings in long distance transmissions and signalto- noise ratio (SNR). The project aims at developing a phase-locked loop FM transmitter with a radius of 5 km for public announcement, the design output is simulated using multisim and PIC simulator. The project serves as information medium for a community of 1000 people instead of town carrier (gongon beating). The announcement passes through a microphone attached to the transmitter, which converts the sound energy to electrical energy; the electrical signal transmitted was received through the antenna of the FM receiver placed within in a range of 2 km-4 km away from the transmitter. A loudspeaker mounted on pole broadcast information. The result of the project demonstrate that the prototype designed consumes 800 mW with a 70 dB output and signal radius of 5 km. The input used was 12-18 V DC with 76.0-76.8MHz frequency range. This accomplished the intended objectives for the community information center. Finally, depending on the availability of further advance technologies, this type of FM Transmitter/Receiver could be further improved with incorporation of sound sensitive circuit in the design for utmost efficiency and reliability in information delivery.