The History of the GPS sytem only dates back a few decades! 

The GPS system we use today was originally designed during the 1970’s and 80’s by the US Department of Defence. Years of development has seen the number of active satellites in the system rise from the initial 24 to around 30.

GPS receivers calculate their position by measuring the distance between itself and three or more orbiting GPS satellites. By transmitting microwave signals and measuring the time it takes for the signal to return from each of at least three satellites, the unit can compute its position by using trilateration.

The military developers of the GPS system originally encoded the signal to be inaccurate by approximately 30 meters, for reasons of national security. This restriction was removed during the Gulf War and GPS has become a popular navigational tool, used throughout the world.

Military uses for GPS include navigation, missile/projectile guidance, search and rescue, target tracking and reconnaissance, as well as forming part of the US nuclear detonation detection system.

Civilian applications include navigation for all types of motor vehicles and marine vessels, surveying, transport vehicle tracking and for synchronisation of the base stations of cellular telephone networks. GPS also provides a precise time reference, useful in the recording and study of earthquakes.

Buying Guide For GPS

• Of course, any GPS unit will get you from A to B. But with the top end devices come sophisticated colour screens, capability for waymarks, landmarks, trip histories and environmental conditions. All of this is delivered with state-of-the-art accuracy.
• At the other end of the scale, basic units have more limited capability, with fewer satellite fixes and simple mapping on monochrome screens.
• When buying a GPS receiver, consider the variety of situations in which it might be used. Will it remain permanently mounted in one boat, or be swapped between vessels, or perhaps used only for hiking?
• For use in a vehicle, or for marine purposes, built-in mapping is required, and the ability to download the latest maps is also desirable.
• The receiver can be permanently mounted and the advantages of such units are larger screens and controls. But a portable unit with a long-lasting rechargeable battery offers greater flexibility when used in multiple vehicles. You’ll also want to look for a unit that can be powered through a 12v car power source.
• Pocket-size units can be a practical choice for hiking, but have the disadvantage of smaller, lower resolution screens which are necessary to save precious battery power.
• Accuracy is important and the more channels a GPS receiver has the more satellites it can pick up. For quicker and more accurate fixes, look for a GPS receiver with a 12 channel system.
• For demanding applications where rough handling is expected, look for a GPS unit with rubber casing. Some receivers are shockproof or waterproof, in varying degrees. And a unit which floats is a desirable feature for the marine sportsman.
• For recording of waypoints and maps, the GPS unit uses its internal memory. At least 8mb should be considered the minimum, with 16 or 32mb desirable for more demanding applications.