M-ary Frequency Shift Keying is a power efficient modulation scheme that is currently used by manufacturers of low power low data rate data transmission equipment. The power efficiency of this modulation increases as the signal alphabet increases at the expense of increased complexity and reduced bandwidth efficiency. There is, however, a gap between the performance of real world systems employing Frequency Shift Keying (FSK) and that of theoretical FSK systems. To investigate the nature of this gap, a comparison is needed between the performance of real world systems using FSK and that of theoretical FSK systems. This thesis investigates the nature of this gap by simulating 2, 4 and 8-level FSK systems in additive white Gaussian noise channel using MATLAB, measuring of the performance of commercially available data transmission equipment manufactured by RACOM s.r.o of the Czech Republic, and comparison of their performances. Some important results have been illustrated and also, it is observed that the gap between the performance of theoretical and real world systems using FSK is about 1 dB at a bit error rate (BER) of 10-3 and widens as BER decreases.