FAQs (Frequently Asked Questions)

What is GPS?
GPS (Global Positioning System) is a navigation technology that provides precise time and location anywhere, anytime and under any atmospheric conditions, by using the NAVSTAR satellites.

How does GPS work?
GPS is a satellite-based navigation system that works by receiving navigation messages from satellites and calculating locations. GPS receivers locate the satellites transmitting the incoming signals and use CDMA (Code Division Multi Access) method to identify individual codes. This means GPS system is able to identify each satellite's unique ID to calculate precise location and navigational data. Here are the steps:

• All satellites have clocks set to exactly the same time
• All satellites know their exact position from data sent to them from the systems controllers
• Each satellite transmits its position and a time signal
• The signals travel to the receiver delayed by distance traveled
• The differences in distance traveled mark each satellite appear to have a different time
• The receiver calculates its own position.

Where does GPS work
Anywhere - as long as the GPS receiver has a clear view of the sky and the antenna is held vertically. Some car manufacturers use athermic heat reflecting windshields which also reflect the GPS signal, blocking it from entering the car. You'll need to use an external aerial if your car has an athermic windshield to re-transmit the GPS signal inside your car.

How much does it cost to run the system once I have installed it?
Nothing! The GPS receiver uses data from satellites in orbit that is free of charge. Manufacturers also release free Service Packs regularly, while maps are updated every 8 to 10 months. Sadly not everything is free, though - there is a charge for these updates.

What affects GPS accuracy?
Many factors affect how accurate your GPS is. The atmosphere, the ionosphere and the position of your receiver could all affect GPS accuracy. Any buildings, natural structures or heavy foliage that obstruct the GPS' view of the sky may decrease the position accuracy. Your GPS accuracy will also depend on your level of clearance with the US DOD. There are two available radio signals that receivers can use: the Standard Positioning Service (SPS) for civilians and the Precise Positioning Service (PPS) for military and authorized personnel. The DOD occasionally jams the GPS signals for civilians on a short-term basis.

What is NAVSTAR?
NAVSTAR is an acronym for Navigation Satellite Timing and Ranging, a name given to the GPS satellite system by the US Government.

How many GPS Satellites are there?
There are nearly 30 navigational satellites orbit the Earth and more might be added. Each satellite makes one Earth orbits every 12 hours. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes (with nominally four Space Vehicles in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane. This constellation provides the user with between five and eight Space Vehicles visible from any point on the earth.

What is WAAS? Why is a WAAS GPS receiver better than the others?
With more and more GPS receivers coming out with WAAS, it might help to understand what WAAS is and how it works better for your GPS. WAAS stands for Wide Area Augmentation System. The FAA states that WAAS is based on a network of approximately 25 ground reference stations that covers a very large service area. Each of these precisely surveyed reference stations receive GPS signals and determine if any errors exist. Each wide area ground reference station in the network relays the data to the wide area master station (WMS) where correction information is computed. The WMS calculates correction algorithms and assesses the integrity of the system. A correction message is prepared and uplinked to a geosynchronous satellite via A ground uplink system (GUS). The message is then broadcast from the satellite on the same frequency as GPS (L1, 1575.42MHz) to GPS receivers, which are within the broadcast coverage area of the WAAS. In a simpler term, WAAS-capable GPS receivers give you better position accuracy by correcting signal errors caused by ionospheric disturbances, satellite orbit errors and other spatial or technical data degradation factors. These GPS receivers will use some of their channels to track WAAS satellites and use WAAS satellite in their position solution.