Glossary
SDR (Software-Defined Radio)
A radio whose tuning hardware digitizes a slice of spectrum so that demodulation and decoding are performed in software.
A software-defined radio combines an RF front end and analog-to-digital converter with a host computer that does the signal processing. Instead of one fixed-purpose receiver, a single SDR can observe many bands and protocols with tools such as GQRX, SDR++, GNU Radio or Universal Radio Hacker.
Key specifications are frequency range, instantaneous bandwidth, ADC resolution and whether the device can transmit (half or full duplex). Receiving is widely allowed; transmitting is regulated and generally requires a licence or strict compliance with licence-exempt band rules.