GPS Navigation - the latest Big Brand GPS units.

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS. The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour.

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. These signals travel at the speed of light. The receiver measures the transit time of each message, and uses the known speed of light to compute the distance to each satellite. These distances, along with the location of the satellites, then determine the location of the receiver through a sophisticated version of trilateration. In most consumer applications, the raw location is converted to a more user-friendly form such as latitude/longitude or location on a map. The time difference tells the GPS receiver how far away the satellite is. 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.

Choose the right sort of GPS

There are several components that need to be looked at when choosing a GPS. There is the GPS receiver (or antenna) itself, which plays an important part. Do you need a seperate Bluetooth antenna unit for clear line of sight?. Then there is the portion of the system which uses the received information to estimate where the device is located on an internal map. Is the GPS unit going to be car mounted or hand-held?

Then there are the various capabilities for route planning and recording, which vary from unit to unit. Some include reversing cameras. Finally, the display portion of each solution type can vary considerably, from limited location information to full color three dimensional maps of the immediate surroundings and advised route.

EPIRB

In the field of Search and Rescue , distress radio beacons, also collectively known as distress beacons, emergency beacons, or simply, beacons, are tracking transmitters which aid in the detection and location of boats, aircraft, and/or persons in distress. In the proper sense, the term refers specifically to the three types of radiobeacons that interface with Cospas-Sarsat, the international satellite system for Search and Rescue. When activated, such beacons send out a distress signal that, when detected by non-geostationary satellites, can be located by triangulation.[citation needed] In the case of 406 MHz beacons which transmit digital signals, the beacons can be uniquely identified almost instantly , and furthermore, a GPS position can be encoded into the signal (thus providing both instantaneous identification and position.) Often using the initial position provided via the satellite system, the distress signals from the beacons can be homed by SAR aircraft and ground search parties who can in turn come to the aid of the concerned boat, aircraft, 4WD or persons.