Spectrum analyzers are used in different areas of electronic industry. From field measurements of mobile and digital television systems to laboratory measurements and the development of next generation of technology. This advanced device enables us to analyse signals of interest quickly, accurately and successfully. It gives us the possibility to simplify conventional measurements. Thus making it easier for us to detect certain failures in the system, which ultimately results in quicker reaction time to resolve the problem. In this paper the fundamental differences between the time and frequency domain are defined. Conversion method from one to another are also mentioned. The advantages and disadvantages of different types of spectrum analysers used today are highlighted. The operating principle of the device, its essential characteristics and the type of measurement it is capable of performing is explained in greater detail and gives us an insight into the range of possibilities that modern spectrum analyzers offer.