Using Real Rf Signals Such As Fm Radio To Teach Concepts In Communication Systems

The theory of communication systems can be made more concrete and interesting by using realworld signals to illustrate the various theoretical concepts. The FM radio signal is, in many ways, an ideal signal to illustrate many of the concepts that are taught in communication system courses. This radio frequency (RF) signal is readily available in most populated areas, the students are familiar with the signal, and most FM stations broadcast both analog audio signals and digital Radio Data System (RDS) signals which can be used to illustrate digital receivers. The RDS signal contains auxiliary information such as the radio station identification, type of program, name of the current song, artist name, current time, traffic reports, etc. The RF signal that is broadcast from local FM radio stations, as well as most other RF signals, can be captured with hardware such as a real-time spectrum analyzer, a vector signal analyzer, or the Universal Software Radio Peripheral (USRP). The analog audio signals can be demodulated in software and used to demonstrate FM demodulation, frequency division multiplexing, double sideband suppressed carrier demodulation, mixing, and filtering. The digital RDS signal can be demodulated using a relatively simple software defined receiver which consists of a Costas loop, matched filter, timing recovery algorithm, and slicer. The FM radio signal can be used in classroom demonstrations or in student projects or homework assignments to enhance a communication systems course, motivate the students with a real-world system, and to provide students with the practical experience of creating and testing a software defined radio receiver.