Construction of a Mobile Frequency Modulation Transmitter

Abstract

A Frequency Modulation (FM) transmitter is an electronic device that produces radio waves with the aid of an antenna. The transmitter generates radio frequency alternating current, that is applied to the antenna. When the antenna is excited by the alternating current, the antenna begins to radiate radio waves by varying the frequency of the radio signal. The transmitter is a Very High Frequency (VHF) Colpitts oscillator capable of transmitting sound to standard FM receiver fitted with a capacitor microphone which picks weak sound signals. This design was achieved using: transistors, resistors, inductors and capacitors. A transmission frequency of ± 5% 100 MHz was used and transmitted up to a distance of 5 metres. The testing of the transmitter was carried out by powering it using a 9 V DC battery and tuning a suitable FM receiver to the transmission frequency of the constructed transmitter. A transmission distance of 5 metres was achieved therefore making it possible to use the transmitter as a portable cordless microphone used for public address (P.A.) systems. The achieved fixed frequency of transmission 56.4 MHz, away from all other radio stations transmission frequencies. This gives the best range and with the least of interferences. With increased power, the range can easily be extended.