Explanation: Digital Signal Processors (DSPs) are the core of modern "software-defined" radios, handling a vast array of signal manipulation tasks. * **A) Control frequency:** DSPs are fundamental to frequency synthesis, often employing Direct Digital Synthesizers (DDS) or controlling Phase-Locked Loops (PLLs) to precisely tune the radio's operating frequency. * **B) Control modulation:** DSPs are used to generate and process various modulation schemes (SSB, FM, digital modes like PSK, FSK, QAM), encoding the information onto the radio wave. * **C) Control detection:** DSPs perform demodulation, filtering, noise reduction, and other signal recovery operations to extract the intended information from the received signal. **D) Control SWR:** Standing Wave Ratio (SWR) is a measure of the impedance match between the radio's output, the transmission line, and the antenna. It's an electrical characteristic of the antenna system, not a signal processing function. While a modern radio might *measure* and *display* SWR (using an external SWR bridge or directional coupler, then feeding that data to the DSP for display), the DSP does not *control* or *adjust* the SWR itself. Adjusting SWR typically involves tuning the antenna or using an external antenna tuner, which are physical impedance matching processes, not digital signal manipulation.