SDR (software-definied radio) is a radio communication system in which the operation of basic electronic components (mixers, filters, modulators and demodulators) is performed by a computer program.
The simplest implementation of SDR may consist of a computer equipped with a sound card or other analog-to-digital converter, and a radio front-end – an electronic circuit that receives a modulated high-frequency signal and transfers it to a lower band within the processing range of the sound card.
A receiver designed in this way can handle various types of radio transmissions only by changing the signal processing program.
Programmable radio is especially useful in rapidly evolving systems that are often subject to modernization and changes in broadcasting techniques – e.g. cellular networks, military systems.
SDR systems are also widely used in colleges and academic research. During classes, they allow students to get acquainted with a wide range of radio systems (analogue and digital), and in research subjects, they allow them to build prototypes and empirical verification of hypotheses.