Before the introduction of GPS, marine navigation was done with a chart, compass and sextant. Learning how to use these instruments was an essential task for every novice sailor. It required good mathematical skills and many hours of study, but things are a little easier for sailors today. The compass and sextant are still important but they have been superseded by the GPS receiver. This amazing device can update its location every few seconds anywhere in the world. Fitting a marine GPS antenna to a vessel improves the strength of the GPS signals and reduces the chance of the receiver dropping out when it is needed.
The Global Positioning System (GPS) is a fleet of space satellites that is used primarily for navigation. Signals from the satellites are picked up by small receiver units, which can be used anywhere on the surface of the Earth. A receiver is able to work out its location from the differences between the various signals. The location is shown on the receiver’s display as a pair of latitude and longitude coordinates. Advanced receivers can also show the location as a marker on a virtual map, as well as keep records of where they have been and make predictions of where they are going.
Just like every other device that uses radio signals, a GPS receiver needs a good antenna to pick up the signals from the satellites. This is especially important during periods of bad weather, when rain and clouds partially absorb the signals and reduce their strength. Buildings, mountains, trees, and other objects also weaken the signals by absorbing and reflecting them. Even waves can cause reception problems if they are large and frequent, so every vessel that travels the oceans needs to have a marine GPS antenna fitted. Vessels that do mostly coastal cruising should also have one fitted, as they often pass near cliffs and other features that cause problems.
The marine GPS antenna looks very different to the whip antenna used for radios. Most models currently available have a plastic dome connected to a short stem, which makes them strangely resemble a large mushroom, but there are also smaller models that look like square blocks of plastic. While it may be tempting to save money by using a whip antenna for a GPS receiver, it probably will not work because it is designed to receive different frequencies. The only feature these antennas have in common is the coaxial cable used to feed the signals to the GPS receiver. Most models are only available in white or black because that is the standard color for marine equipment.
There are two main types of marine GPS antenna: passive and active. The main difference between the two types is that an active antenna has an amplifier, which boosts the power of the signal before it’s sent through the coaxial cable to the receiver. An active antenna is generally better to have, but it’s more difficult to install because it needs a separate power cable for the amplifier. The other features to look include a high gain, low noise, and solid construction. In particular, the plastic dome needs to be very tough to survive in the harsh marine environment for many years. Also, look for an antenna that has coaxial cable and a mounting bracket included in the box, as these can be expensive to buy separately.
There are two ways to install a marine GPS antenna, but it will usually be designed for just one way. One type is designed to be attached to the mast or rigging with the aid of a bracket, while the other type is designed to be installed through the deck or cabin roof. Before punching any holes in the vessel, it is important to choose a location that is away from winches and other equipment that may interfere with the antenna. Also, avoid locations that are in the way of people moving around the deck, to protect the antenna from being broken.