VHF/HF/MF

• VHF(Very High Frequency): Radio waves in the range of 30MHz-300MHz, mainly propagate along a straight line path, significantly affected by the curvature of the Earth, resulting in relatively short propagation distances. This propagation method is called line-of-sight propagation, suitable for near-coastal communication for ships within 30-50 nautical miles.

• HF(High Frequency): Radio waves in the range of 3-30MHz can achieve long-distance communication through ionospheric reflection. Suitable for long-distance shortwave communication, such as ships navigating in A4 sea areas.

• MF(Medium Frequency): Radio waves in the range of 300KHz-3MHz can be reflected between the Earth's surface and the atmosphere for near and medium-distance alarms and communications.

  
  

VHF, MF/HF Equipment

• VHF Equipment: Radio communication equipment for telephone communication and digital selective calling (DSC) in the frequency range of 156-174MHz, located near the navigation command position. It includes:

• VHF DSC radio telephone equipment: Provides short-range frequency modulation (FM) radio telephone and DSC calling, as well as DSC distress alerting.

• Portable two-way VHF radio telephone equipment: Provides relatively short-range FM and radio telephone communication in case of distress, serving as the only communication equipment after abandoning the ship onto lifeboats.

• VHF EPIRB: Specifically designed for DSC distress alerting.

• MF/HF Equipment: MF provides medium-distance single sideband (SSB), NBDP, DSC calling, and DSC distress alerting. HF provides long-distance SSB, NBDP, DSC calling, and distress alerting. In GMDSS, HF communication can replace satellite communication, especially outside satellite coverage areas where HF communication is the only long-distance communication method. Equipment includes: SSB MF/HF, MF/HF NBDP, HF MF/HF DSC, etc.

Applications of VHF, HF, MF in distress alerting equipment in various sea areas