doi:10.3850/978-981-08-7302-8_0785

ABSTRACT

A Wireless Data Modem using Tele Typewriter Signals and Frequency Shift Keying (FSK) Modulation Technique is proposed here in order to avoid inter-symbol interference. Basically a Modem sends and receives Digital data signals to and from various Computer Networks and peripheral devices. The Wireless Modem designed here consists of 4 stages namely a) Modulation stage, b) Transmission stage, c) Reception stage and d) Demodulation stage. The Modulation stage consists of IC 555 Timer working in Astable Mode and generating Frequency Shift Keying (FSK) signals. Transmission is Wireless and is achieved using IR LED. The Transmitted signal is received using a spectrally matched Phototransistor. Demodulation is achieved using IC565 (Phase Locked Loop) which recovers the input message signal. The modem designed here makes use of Tele Typewriter signals which avoids inter-symbol interference. The Bandwidth of such Tele Typewriter signals is 200Hz. For signals with such lower bandwidth Frequency Shift Keying (FSK) is the best Modulation Technique for transmitting digital information. The overall Noise Figure for this Wireless Data Modem is high with zero Bit Error Rate. Hence the whole setup is Stable and accurate device for transmitting digital data.

Keywords: Frequency shift keying (FSK), Tele typewriter signals, Inter-symbol interference, Phase locked loop, Baud rate, Bit error rate.

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