Antennas · VHF propagation · Installation
For marine VHF, a few extra metres of antenna height can matter more than a large increase in transmitter power. The reason is geometry: VHF coverage is governed mainly by the radio horizon.
VHF follows the horizon
Marine VHF normally travels in near line-of-sight paths. Raising either antenna extends the distance to the radio horizon. IMO planning criteria express range as a function of the square roots of shore and ship antenna heights.
Power cannot lift an antenna
More power can improve signal strength at the edge of coverage, but it cannot reliably transmit through the curvature of the Earth. A low antenna driven hard may still be outranged by a modest transmitter connected to a clear, elevated antenna.
Reliable communication is not measured by how much was transmitted, but by what the receiving side can understand and act upon.
Placement includes the surroundings
Conductive structures, other antennas and high-power equipment can affect performance. IMO guidance recommends elevated, unobstructed locations, suitable separation, vertical polarisation, low-loss screened cable and weatherproof outdoor connections.
The installation is a system
Antenna, feed cable, connectors, ground arrangements, power supply and radio all contribute. Height does not excuse damaged coax or corroded connectors. The useful comparison is never watts versus height alone, but the complete path from transmitter to antenna and onward to the receiving station.
