How to pick the perfect VHF antenna for your boat, and your price point.
An antenna’s gain is a measurement of its focused radiation and sensitivity pattern in a given direction as compared to that of a theoretical “isotropical” antenna, which would be able to radiate electromagnetic waves in all directions at the same time without losing any range, essentially creating an infinitely large “globe” of waves. Gain is measured in decibels (dB), which generally move up in increments of three. An isotropic antenna would have a 0 dB gain, while a six-inch handheld antenna might have a 1 dB gain, with a weak signal that travels away from the antenna in a near-globe-like pattern—though with conical chunks taken out at either end of the antenna where the signal does not transmit. As the antennas get longer, and thus taller, the wave patterns flatten out, transmitting signals aimed closer and closer to the horizon. This process greatly enhances the antenna’s gain. As a rule of thumb, a four-foot antenna will have about a 3 dB gain, an eight-foot antenna will have 6 dBs, and a 16-footer will have a 9 dB gain.
The first, and most obvious, factor in VHF antenna price is length. Antennas can range from a few inches long on handheld VHFs to over 20 feet. The advantages of a handheld are fairly evident, particularly on a smaller craft—portability alone being a major plus. However, its range will be noticeably and significantly shorter than longer antennas since VHFs are line-of-sight transmitters and so must be able to “see” the antenna of the station with which they are communicating. That said, the meager amount of materials used to construct a smaller antenna, and its relatively simple construction, make it much cheaper than a longer one. Furthermore, handhelds usually only have one “element,” the metallic guts of an antenna that do the actual receiving and transmitting, which also keeps their prices down. Longer antennas often have elements stacked one on top of the other in a labor-intensive process called “collinear phasing,” which can send both their signal strength, and their price, into increasingly far-off orbits.
Construction also plays a key role in determining price. There are four main elemental cores used. In ascending order of durability and signal strength, as well as price, they are copper wire, brass tubing, copper and brass tubing, and silver-plated brass tubing. (The least expensive material for an antenna is a bare, stainless steel wire whip, which you can purchase for under $100. Normally no more than three feet long to avoid excess bending, whips are usually found on smaller vessels such as sailboats, ski boats, and bass boats.) There are two reasons for the escalation in price. First, tubing requires more raw materials and labor than a simple wire element. Second, larger-diameter (and more expensive) tubing is used to increase the bandwidth for more effective communicating at the extreme ends of the frequency band (156.050 MHz on one end and 162.525 MHz at the other) making antennas with tubing that much more efficient.
However, length, diameter, and materials are not the only factors that affect cost. Since the elements are relatively delicate, they need to be protected from weather and the errant dings and nicks that are part of the maritime life (that mostly means run-ins with bridges). So most VHF antennas are wrapped in protective material that will prolong their lives but also inflate their price. Perhaps the most important of these layers is the outer fiberglass shell, which not only guards the elements against bumps and bruises but also keeps out moisture. Directly underneath the fiberglass is a layer of low-loss ethafoam, which is a foam-rubber material that cushions and supports the antenna without interfering with its signal.
So what’s the right antenna for you? If your boat is either large enough to resist rolling in most conditions or not used in waters where rolling is an issue, a high-gain antenna is best, as it will maximize your range without shooting its horizon-aimed waves uselessly off into the atmosphere. If you’re in a boat that tends to roll and heel, you’ll want a medium-gain antenna because it will have good range and be able to transmit signals to low-lying landmasses, even in swells. A low-gain antenna is best for handheld radios as they are almost never held vertically and are often used in small boats that are easily tossed, and so must transmit signals from all different angles.
Digesting all of this technical information, you’ll be equipped to communicate what you want to the marine-supply salesman so you can communicate how you want out on the water.
This article originally appeared in the June 2011 issue of Power & Motoryacht magazine.