Personal digital assistants (PDAs) are handheld devices that were originally designed as personal organizers, but became much more versatile over the years. Like a pc, it is possible to install additional software on most PDAs. Software can be bought or downloaded from the Internet, allowing users to personalize their PDAs to their liking. Some PDAs also allow for adding hardware and PDA Sat Nav is possible with a GPS receiver turning the PDA into a Sat Nav unit which can be handheld or fitted to a vehicle.

 

GPS is the world’s first satellite navigation system. It was developed by the U.S. Government’s Department of Defense, who gave GPS its official name: the NAVSTAR system (Navigation Satellite Timing and Ranging).

GPS consists of 3 key elements:
 

• Satellites in space
• Monitoring Stations on Earth
• And last but not least, you and your PDA sat nav GPS receiver.

 

The satellites
GPS has 24 satellites that circle Earth in six orbital paths, sending out radio signals from their position in high orbit, 12,600 miles/ 20,300 kilometres above our heads. Being so high, each satellite’s signal covers a large area of the earth’s surface and their orbits have been ‘choreographed’ so that your PDA GPS receiver back on Earth is always getting signals from at least 4 satellites, the number you need to pinpoint your location.

 

The monitoring stations
There are 5 monitoring stations: the master station in Colorado Springs, USA and four unmanned stations. One on Hawaii, the other three in remote locations as close to the equator as possible: Ascension Island in the Mid Atlantic; Kwajalein in the Pacific and Diego Garcia Atoll in the Indian Ocean. The 4 unmanned stations receive constant data from the satellites and forward it to the master control station, which ‘corrects’ the data and then sends corrected data back up to the GPS satellites.

 

GPS signals
Your PDA Sat Nav GPS receiver picks up signals from GPS satellites to work out your location. The last, important step in the process is of course you making use of that information. Each satellite transmits low power radio signals on different frequencies for different users. The signals travel by so-called ‘line of sight’. This means they pass through clouds, glass and plastic, but not usually through solid objects, such as buildings.

Initially GPS was only intended for military use. But then tragedy struck. On 1st September 1983, Korean Airlines flight KAL007 from Anchorage to Seoul strayed off course into USSR airspace and was shot down by a soviet Su-15 fighter jet. All 269 passengers and crew were killed. Two weeks later, US President Reagan proposed GPS be made available for civilian use to avoid navigational error ever again leading to such a catastrophe. While by no means the only reason, the Korean Airlines disaster was certainly a major catalyst toward civilian access to GPS.

 

GPS has become a vital global utility, indispensable for modern navigation on land, sea, and air around the world, as well as an important tool for map-making, and land surveying. PDA Sat Nav GPS also provides an extremely precise time reference, required for telecommunications and some scientific research, including the study of earthquakes.