Development of a low-cost frequency shift keying signal Transmitter for digital signal processing

摘要

A transmitter consists of an oscillator that generates a carrier frequency followed by a buffer amplifier which provides a high impedance load to minimise drifts, and modulated with an amplified intelligence signal. The development of a low cost frequency shift keying (fsk) transmitter is the concern of this work. The fsk signal forming the base band signal is low - level modulated with a carrier, within the mark and space frequencies. The output from the frequency shift keying circuit at a space frequency of 10kHz and a mark frequency of 20kHz was modulated with a 500kHz single frequency carrier using a diode AM modulating circuit. The transmitter circuit was designed with the use of active devices with few passive components. The measured resonant frequency is 478.63 kHz at 13.427dB, while the calculated resonant frequency is 485 kHz. The calculated carrier power is 1.62W, and the total power radiated out from the antenna is 2.35W. The signal noise was calculated to be 5.228dB while the measured signal noise was 5.399dB. The amplified signal is connected to an antenna, with the response of the design simulated on Multism -12 application software. This development can be used to encode digital signals for information transfer in an area within a 5 kilometre radius with precision.