Marine VHF, GPS, and satellite antenna basics

Marine antenna selection drives radio performance more than radio choice. VHF antennas rated by dB gain: 3 dB (short 3 ft or emergency), 6 dB (standard 8 ft, most sailboats), 9 dB (17-23 ft fiberglass whip, most motoryachts), higher gain compresses the signal beam vertically, which extends range on flat water but goes blind in heavy seas as the antenna rocks. Rule: 6 dB for sailboats and rough-water cruisers, 9 dB for motoryachts that stay upright. Mounting: as high as possible, isolated from the mast on sailboats (a mast is an obstruction), 4 ft minimum from radar dome. Cable matters: RG-58 for runs under 20 ft, RG-8X for 20-50 ft, LMR-400 or heliax for 50+ ft. A cheap thin coax at 8 dB gain equals a 5 dB antenna. GPS antennas are simpler, nearly all marine GPS is L1 band, active (contains a preamp), needs 12V from the receiver. Position matters: no obstructions above 15 degrees horizon, no proximity to inductive loads (autopilot compass, radar rotator) which cause dropouts. Satellite TV (KVH, Sea Tel): gyro-stabilized dish, requires a clear sky view above 15 degrees latitude-corrected elevation. Modern flat-panel VSAT (Starlink Maritime especially) has replaced most legacy satellite TV on recreational yachts, cheaper, faster, less maintenance.