Which statement describes a passive injector?

A passive injector is a device that adds power to a transmission medium like a CAT-5e cable without requiring an external power source to operate itself. The defining characteristic of a passive injector is that it supplies direct current (DC) voltage onto the cable to power devices like network cameras or wireless access points.

The choice describing the function of a passive injector accurately highlights its role in delivering DC voltage, thereby allowing powered devices to operate without needing their power adapter present at the device's location. This capability is instrumental in scenarios where cabling infrastructure is already in place, thereby simplifying installations in networking environments.

In contrast, other options imply functionalities that do not align with what a passive injector does. For instance, while enhancing signal strength is a critical aspect of network performance, a passive injector does not amplify signals on its own and relies on the existing power from the DC voltage it injects. Similarly, filtering out DC voltage or acting as a power amplifier are functions more characteristic of active devices, which do require external power to perform and are not typical roles for a passive injector.