For which vessels are GMDSS regulations compulsory

In line-of-sight communication airborne elements such as rain, fog and snow can all affect communication quality. Of these weather conditions, rain has the greatest effect on VHF data transmission .

How can I expand the range?

A longer wavelength , which corresponds to a lower frequency, as a general rule lets a radio signal travel a greater distance. Lower frequencies or longer wavelengths also have greater penetrating power.10 Eki 2016

Key Points. The key factors affecting communication range are: antenna, obstructions, signal strength (wattage), and signal type .