Final answer:
A repeater is the correct answer to the question, as it receives a low-frequency signal and retransmits it at a higher frequency or power level to cover longer distances.
Step-by-step explanation:
A device that receives a low-frequency signal and then transmits it at a relatively higher frequency is known as a repeater. This electronic device takes in a weak or low-level signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Repeaters are often used in wireless networking to extend the range of a signal.
A duplex refers to a type of communication that allows two-way communication to happen simultaneously. A scanner is a device that scans documents and converts them into digital data. A receiver is a device that receives signals but does not necessarily amplify or increase their frequency.