What is GPS?

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.

How it works?

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. 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.

How quick is my GPS receiver?

In today’s world, we expect everything to happen NOW! - GPS is not always like that.

 “Why is it taking so long? What’s going on?” we hear you ask.

Your GPS receiver is trying its best. Sometimes that may seem too slow for us. Do you always jump into your daily tasks straight out of bed? Or are you sometimes a little sluggish, and need a kick start? GPS receivers are like people and need care and a little understanding at times.

Let’s give it the benefit of the doubt, and look at what could be happening. Your GPS receiver is in one of three states of readiness.

Frozen start - It’s straight out of the packing box for the first time. Or it’s been doing a Rip van Winkle for the past few weeks. In either case, it does not have a recent navigation message and/or current position in its memory. Getting this information is called ‘Initialization’. Unfortunately it may take up to 15 minutes

for your first position fix. So sit back and relax.

Cold start - Your GPS receiver is either trying to use an old navigation message or has been moved more than 300km since the last time you used it. You should only have to wait up to 5 minutes for your first position answer.

Warm start - Your GPS receiver has both a recent navigation message and is less than 300 km from its last position. It should be up and running in a minute or two.4

What about trees and things?

The radio transmissions from the satellites have traveled some twenty thousand kilometers before they reach the antenna of your GPS receiver. We should not be surprised to learn that the signals are weak and easily interrupted. A completely clear sky, free of buildings and trees, such as at sea or in a desert, with nothing to interfere with the signals, is the best.

Sources of GPS signal errors

Factors that can degrade the GPS signal and thus affect accuracy include the following:

• Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
• Signal multipath — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
• Receiver clock errors — A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors.
• Orbital errors — Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
• Number of satellites visible — The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
• Satellite geometry/shading — This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
• Intentional degradation of the satellite signal — Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.

Regarding the battery

The GPS receiver chip in the unit cost many power, so that please keep using the AC charger or Car charger when navigating via the GPS unit. Otherwise the power would not last longer...