What type of systems are used to enhance radio transmissions limited by distance or obstacles?

Repeater systems are specifically designed to extend the range and improve the reliability of radio communications that may be hindered by distance or physical obstacles such as buildings or terrain. A repeater works by receiving a weak or low-level signal and retransmitting it at a higher power, allowing the communication to cover greater distances or penetrate through barriers.

In the context of firefighting and emergency services, effective communication is crucial. Repeater systems ensure that first responders can maintain contact with dispatch and each other, even in challenging environments. This capability is particularly important in large-scale emergencies or operations in urban or mountainous areas where typical radio signals might struggle to connect.

The other options—duplex channels, trunking systems, and simplex channels—serve different purposes in communication systems. Duplex channels allow for simultaneous two-way communication, trunking systems manage multiple communication channels to optimize frequency use, and simplex channels support one-way communication without the ability to respond or converse back. While these systems have their place, they do not specifically address the enhancement of radio transmissions limited by distance or obstacles like repeater systems do.