What is the most common type of antenna for GMDSS VHF?

The most common type of antenna for Global Maritime Distress and Safety System (GMDSS) VHF operations is indeed not represented by the provided options as the answer indicates. GMDSS requires reliable communication, especially for safety at sea, which necessitates antennas specifically designed for effective performance in that frequency range.

Typically, a VHF antenna utilized in GMDSS setups is a vertically polarized, omnidirectional antenna. This type of antenna is optimized for VHF frequencies (usually around 156 to 162 MHz), which are essential for maritime communication. The vertical polarization helps in minimizing the effects of multipath interference that can occur in maritime environments, ensuring clearer and more reliable communications.

The other antenna types mentioned, such as horizontally polarized circular antennas and long wire antennas, do not meet the specific requirements and effectiveness needed for GMDSS VHF operations. Horizontally polarized antennas can be less effective at maritime distances due to how signals propagate over water, while long wire antennas are generally suited for lower frequency operations, not for the VHF maritime band. The focus on VHF communications, coupled with the need for suitable directionality and polarization, illustrates why the selection of a vertical omnidirectional antenna is critical in this context.