Which of the following is characteristic of J2B mode?

J2B mode refers to a specific type of modulation used in radio communications, particularly in the context of the Global Maritime Distress and Safety System (GMDSS). It is characterized by amplitude modulation (AM) where the modulating signal consists of single tones, which can be used for automated identification and signaling purposes.

When a system is operating in J2B mode, it essentially leverages the principles of single-tone amplitude modulation, allowing for efficient transmission of information such as distress signals or navigational data. The use of a single tone means that the transmission is focused and does not include complex signals, making it easier for receivers to accurately decode the intended information.

This distinct characteristic emphasizes the simplicity and efficiency of J2B mode, particularly for sending critical information in maritime operations where clarity and reliability are paramount. Other potential configurations mentioned, such as multiple tones or the presence of sidebands, are not relevant to the definition of J2B mode, highlighting why the correct response clearly identifies the unique feature of amplitude modulation with single tones.