Which mode occupies the least bandwidth?

The mode that occupies the least bandwidth is one that transmits data using narrowband techniques. In this case, J2B is a form of single-sideband modulation with vestigial sideband and is used for voice communications. It has a narrower bandwidth compared to the other modulation types listed.

In contrast, H3E and A3E modes are forms of amplitude modulation (AM), which generally require a wider bandwidth due to the nature of how they transmit audio signals, encompassing full sidebands. F3E, which refers to frequency modulation (FM) used for voice signals, also typically consumes more bandwidth than J2B due to the broader range of frequencies its signal covers.

Consequently, understanding the characteristics of these modulation types indicates that J2B utilizes its spectral efficiency effectively, allowing it to lessen the amount of bandwidth needed for transmission while still effectively conveying voice data.