Software-defined radio
lastmod 2025-07-11created 2025-07-111 edits
SDR (Software Defined Radio) is a technology that handles the modulation and demodulation process in wireless communication through software.
Conventional modulation/demodulation circuits were physically built circuits, so apart from changing frequency or gain by adjusting RLC elements, there were almost no controllable elements. This made it hard for a single device to use multiple communication methods or cover a wide range. To overcome this, quite complex structures were adopted, such as building multiple modulation/demodulation circuits.
Later, once digital modulation/demodulation through semiconductors became possible, and direct RF processing became possible with highly responsive, high-throughput devices such as FPGAs and with DSPs, SDR emerged by using these to replace RF processing in the back end. The principle is as follows: on the transmitting side, the signal to be sent is synthesized and modulated into digital data by a computer or DSP, converted into an analog signal by a D/A converter, frequency-converted to a high frequency that can be transmitted as radio waves, greatly amplified in output, and then transmitted through the antenna. Conversely, on the receiving side, the weak analog high-frequency carrier signal received by the antenna is lowered to a suitable intermediate frequency (superheterodyne), linearly amplified to a suitable strength, the complex waveform is sampled by an A/D converter to create a digital signal, and the signal wave is then extracted through demodulation matching the various modulation schemes. Past analog modulation/demodulation circuits had fixed functions as physical circuits, but SDR modulates and demodulates with a digital signal processor using software algorithms, so it can be changed freely and even complex modulation schemes can be applied easily.
If this goes further, replacing everything from the antenna to the front end so that the DSP receives and processes the signal directly from the antenna, it becomes Software Radio.
See also
- Flipper Zero
- Flopper Ziro - DIY open-source Flipper Zero clone