VHF radio range is line of sight, so height is a very important factor in achieving maximum range. On a sailing boat the most suitable antenna location is, therefore, at the top of the mast. Two boats, each with a masthead antenna 60’ above sea level can theoretically communicate at about 22 miles. (Much greater ranges are possible when atmospheric conditions are right, but this cannot be relied upon). A transmitter at a coast station, perhaps 1000 feet above sea level, could communicate with these same boats at closer to 50 miles. On a power boat you have to do what you can to place the antenna as high as possible above sea level.
A penny in the antenna is worth a pound in the radio. It is important to select the right antenna and install it in such a way that it maximises the performance
of the radio or AIS transceiver to which it is attached.
Selecting an antenna:
For boat applications you would select a 3dBi antenna because it gives a nice fat, round signal pattern and this is important because on a moving boat you want the best chance of some of the signal being directed at the horizon and not the sky or sea.
You can get more focused antennas, 6dBi or 9dBi, but these antennas have a tight disc-like signal pattern and are unsuitable for the constantly moving platform of a masthead located antenna.
Other criteria for selecting a marine antenna, particularly one for masthead mounting, would be:
• Resistance to UV degradation. Clearly all stainless steel construction wins hands down.
• Resistance to bird strikes. Again, a stainless steel whip is less vulnerable than a rigid plastic
• Ability to be removed when the mast is taken down. This is when the antenna is particularly vulnerable and those with factory crimped connections cannot be removed without removing all the cable with them. The connection at the antenna should be an SO239 socket which takes the standard PL259 connector.
• Low weight.
• Sturdy mounting bracket.
The Metz VHF antenna satisfies all these criteria. Its excellent durability as a result of stainless steel construction combined with superb performance makes it the choice of the US Coastguard and UK Search & Rescue services, the Clipper Fleet, many charter companies and thousands of leisure sailors all over the world.