Radio Equipment, Antennas, and Basic Electrical/Radio Principles
VHF versus HF
Marine VHF is frequency-modulated (FM) in the 156–162 MHz band and travels essentially line-of-sight; range is governed by antenna height far more than by transmitter power (typically 25 W high, 1 W low). Marine HF uses single-sideband (SSB, class J3E) between roughly 2 and 30 MHz, propagates by ground wave and skywave, and reaches hundreds or thousands of miles - but it needs a good ground and often an antenna tuner. Channel 70 (156.525 MHz) is DSC only; no voice is permitted there.
Antenna and feedline practice
Use a vertical, vertically polarized antenna with an adequate ground plane or counterpoise; a poor ground is the classic cause of a weak or erratic signal. Feedline is 50-ohm coaxial cable with PL-259 connectors kept dry and tight. Never key the transmitter with no antenna connected - reflected power can destroy the output stage. A high SWR indicates a mismatch: check connector, cable, and ground before blaming the radio.
Power and basic electricity
Small-craft radios run on 12 V DC. Fuse the positive lead at the battery, observe polarity, and keep cable runs short and heavy enough to limit voltage drop. Ohm's law: V = I × R. Power: P = V × I.
Rule of thumb: wavelength in metres ≈ 300 ÷ frequency in MHz. Channel 16 at 156.8 MHz gives about 1.9 m, so a quarter-wave whip is roughly 0.48 m. Know the beacons too: a 406 MHz EPIRB alerts the satellite system and transmits 121.5 MHz for homing; a SART responds on 9 GHz to a searching radar.
Traps: attributing long range to wattage alone, treating AIS or an EPIRB as a voice device, and forgetting that DSC requires a programmed MMSI.