What is a radio transmitter that broadcasts a signal in all directions called?

A radio transmitter that broadcasts a signal in all directions is referred to as a non-directional beacon station. This type of transmitter does not focus its signal in any specific direction, providing coverage uniformly across the surrounding area. Non-directional beacons are primarily used in aviation and maritime navigation to help pilots and mariners determine their position and maintain orientation.

The signal from a non-directional beacon can be received from various angles, making it a reliable reference point for navigation. In contrast, directional beacons focus their signals in specific directions, which can be useful for certain navigation purposes but do not provide omnidirectional coverage. Repeaters are used to extend the range of communication by retransmitting signals, and the term "common transmitter" is not a recognized classification in this context. Thus, identifying a non-directional beacon station accurately captures the essence of a transmitter that broadcasts signals uniformly in all directions.