Design And Construction Of An Audio/video Transmitter

ABSTRACT

The design of the wireless audio and video transmitter was done in stages taking into consideration a pre-selected desired frequency. These stages are the power supply stage, the carrier frequency generation stage, the carrier frequency pre-amplification stage, the voltage controlled oscillation stage and the final stage which is the modulation and amplification stage. First, carrier frequency was generated in the oscillator circuit comprising of an NPN transistor Cl 674, a variable capacitor connected in parallel with an air-filled inductor to fo1m a tank circuit and biasing resistors. The carrier frequency generated is then amplified in the next stage by the same Cl674 transistor which acts there as an amplifier. The audio signal is modulated in the next stage which is the Voltage Controlled Oscillator (VCO) that generates a base frequency of 5.5

MHz. The video and audio signals are superimposed at the final stage and transmitted to the air through an antenna. The project is based on radio frequency propagation and the medium is free space. Power is supplied to all stages by a full wave rectifier circuit comprising of a transformer, four diodes that forms the rectifier and filter capacitor. Zener diodes were used in regulating the voltages supplied to the oscillator stages because variation of voltage is undesirable. The transmitted signal would be received by a television receiver by tuning to the Ultra High Frequency (UHF) range between 470 to 960 MHz.