Satellite navigation systems always use radio time signals, which are transmitted by the satellites in order to enable mobile receivers on the ground to determine their exact location. It is due to the relatively clear line of site between the satellites and receivers on the ground. Which are combined with ever-improving electronics and allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time. An early time the predecessor was used as a ground based Loran and Omega systems, which were used by terrestrial long wave radio transmitters instead of satellites. The first satellite navigation system was deployed by the US military in the 1960s.
In the present time the best necessary satellite navigation system is the Global Positioning System (GPS), which is nothing but a satellite-based navigation system, was made up by the help of a network of 24 satellites. It was placed into a fixed orbit by the U.S. Department of Defense. GPS satellites are powered by the solar energy. They have many backup batteries onboard, to keep them running in the event of a solar eclipse, when there's no solar power. There are many Small rocket boosters on each satellite keep them flying in the correct path. Due to this GPS works in any weather conditions, also it is able to works anywhere in the world and 24 hours a day. GPS satellites circle the earth twice in a day, in a very calculative orbit and transmit signal information in to the earth. The GPS receivers take all this information and use triangulation to calculate the user's exact location. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map in a suitable way. GPS unit can calculate other information like speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.
At the time of choosing any GPS devise you have to be careful about many things such as, Price, Features, Maps and Brand etc. Here is many satellite navigations product which available in the market in a very low cost such as: Garmin Nuvi 265W, Garmin Nuvi 255, TomTom ONE v4,TomTom XL Satellite Navigation System , Navman F45 Widescreen Satellite Navigation System etc.
Read more: http://www.articlesbase.com/gps-articles/how-to-choose-a-best-sat-nav-systems-3272562.html#ixzz0zgZ2kr7J
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