In which frequency band does a search and rescue transponder operate?

The correct answer is the frequency band at 406 MHz. This frequency is specifically designated for emergency distress beacons, including search and rescue transponders, because it is part of the international COSPAS-SARSAT satellite system. The 406 MHz signal is utilized by emergency beacons to transmit alerts to satellite systems and ground stations, allowing for rapid location and assistance to individuals in distress.

The other frequencies mentioned do not pertain to search and rescue transponders. For instance, S-band frequencies, which range from about 2 to 4 GHz, are primarily used for radar, communication, and some satellite services, rather than for search and rescue operations. Similarly, the frequencies of 3 GHz and 9 GHz fall outside the designated emergency distress bands and are typically associated with other telecommunications and radar applications. Therefore, 406 MHz is specifically aligned with the needs of search and rescue operations and is recognized internationally for this purpose.