Antennas

Revised by BoatUS editors in April 2012

VHF AntennaThe higher the rated gain of your antenna, the longer the range, and the narrower the beam. The transmission range, however, depends more on the height of your antenna than any other factor, including wattage. The higher the antenna, the greater its "line-of-sight". The only way to legally increase the sending and receiving power of your marine radio system is to use a longer antenna with more gain.

Gain is the ability of an antenna to amplify both outgoing and incoming signal power. It's a function of how much the antenna focuses the energy of the signal in a horizontal direction. When gain (measured in decibels, or dB) is increased, the normally oval radiated power pattern becomes more oblong and horizontal, reaching out further toward the horizon. Increasing gain increases your signal power geometrically: a step from 0dB to 3dB will double your signal's power, while a step from 3dB to 6dB quadruples it. Higher gain also means a more narrowly focused beam, which can cause the signal to fade in a rolling sea. The more stable your boat's platform, the less it rolls, and the higher the gain you can effectively use.

Coaxial cable is specially designed to transfer your radio signal to your antenna with as little power loss as possible. Use the largest 95% shielded coax that fits to reduce signal loss between the radio and antenna. PVC-coated (not plastic) cable RG-58 and RG-8X, frequently supplied with the antenna, are fine for cable runs up to 25'. For longer runs, use low-loss cables such as RG-8 or RG-213. RG-8U is not recommended for marine applications because it is foam-filled and will collect moisture, creating loss and quickly corroding the cable inside. Keep the cable run as short as possible and avoid sharp bends, kinks, or strains to get the most from your system.

The ferrule is the bottom fitting on the antenna that threads into your antenna mount. A plastic or nylon ferrule may be adequate on small boats for light use in calm or moderate waters, but it’s always preferable to use high grade stainless fittings. Use silicone or other quality anti-corrosion spray regularly on both the ferrule and the mounting threads to prevent corrosion.

The connection between your radio and antenna is critical to your VHF system's operation. If you must splice the cable, use proper PL-259 connectors to reduce loss. Use a silicone protectant spray or clear semiconductor heat shrink compound, and wrap them in Ancor Marine Grade - heat shrink tubing or quality vinyl electrical tape to prevent moisture intrusion, which will corrode the copper braid in the coax.  Immediately seal up any nicks in the cable and antenna to keep moisture out. Many connectors today do not require solder. However if you must solder, use proper soldering techniques and at least a 30-watt soldering iron and 60/40 rosin core solder. This job is not difficult, just exacting. If it's beyond your abilities or patience, hire a professional. Poor connections mean poor to no radio performance.

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