What is a key characteristic of portable radios used in fire departments?

Portable radios used in fire departments are designed to ensure effective communication in various environments and situations encountered during emergency operations. One key characteristic of these radios is their range, which is approximately one mile. This range allows firefighters to communicate effectively within a typical urban environment or a confined incident area.

In practical terms, the estimated one-mile range takes into account various factors that can influence communication, such as physical obstructions (like buildings or trees), frequency interference, and atmospheric conditions. This performance is particularly vital during emergency responses where maintaining communication with team members is crucial for safety and coordination.

The other options suggest features that do not accurately describe portable radios. For instance, the notion of operating at 100-150 watts is more aligned with base station or higher power radios, as portable radios generally have lower transmission power for better portability and battery efficiency. Similarly, the idea that these radios operate only when held in a straight position ignores the flexibility required in fieldwork. Additionally, the statement regarding unlimited receiving power does not reflect the functional limitations present, as the effective range for receiving signals is also subject to similar constraints as transmission capabilities.