What is the signal transmitted in J2B mode?

In J2B mode, the signal transmitted consists of an upper sideband that conveys two alternating tones. This mode is typically utilized for transmitting navigational and other essential information in maritime communications via the GMDSS (Global Maritime Distress and Safety System). The use of upper sideband helps in better signal clarity and reduces the bandwidth needed for transmission compared to methods that might transmit both sidebands.

The concept of transmission involving alternating tones is crucial for signaling and communication efficiency. In J2B, one tone represents an active signal, while the alternation allows for encoding additional information within the same frequency band. This method is particularly useful in marine environments where clear and reliable communication can be critical for safety and coordination.

The options that involve full carriers or two sidebands do not accurately represent J2B's encoding method, which specifically aims for efficient signaling using limited bandwidth. As a result, understanding the nature of J2B's use of alternating tones in upper sideband transmission is key to grasping its role in maritime communication.