Knowing a little of how GPS systems work will make you more appreciative of their complexity and make you less likely to balk at the cost. GPS systems are added and more often, standard features in the latest cars, PDAs (Personal Data Assistants) and cell phones. This writer isn t an engineer or scientist, so this article is a summary of how GPS systems operate. For more technical details, read something else.

<

p>Here We Go

<

p>There are some 2500 satellites currently in orbit around the Earth. Quite a large percentage of them are GPS system satellites. Only about 36 actually are operative the others are retired GPS satellites. They constantly transmit a low-power radio signal to Earthly GPS receivers (not the other way around). By passing four of the receivers or more, the GPS satellite knows where it is.

<

p>GPS systems satellites are about seventeen feet across when their solar power panels are fully spread out. Yes, they run on solar power, as well as the Earth s gravitational field. They are built to last ten years (knock on wood). The oldest is from 1978. That one goes around telling all the younger GPS systems satellites how hard it was in his day and how lucky the younger ones have it.

<

p>But Seriously

<

p>So what is a GPS receiver? It s whatever GPS device is bopping about on Earth. One could be on a commercial cruise liner, another in a taxicab and yet another in your boss s hands. The average cost of a personal GPS systems receiver is about $300. Considering you didn t have to pay to design, build and launch the satellite into space is, $300 is a pretty reasonable price.

<

p>Still, there are things that can interfere with your GPS device. The GPS systems satellite can transmit through clouds, atmosphere and the ring tones of everyone else s cell phones, but there are some things that can goof up the transmission. Mainly, these things are solid objects. This is a slight snag that is being improved upon all of the time. Going outside, rolling back a sunroof, avoiding trees can help a fuzzy signal clear up.

<

p>And you don t have to worry about stumbling onto any nation s secret invasion plans. There are separate signals for civilian GPS systems. Military GPS systems use a different signal. The US Department of Defense used to require a GPS satellite to intentionally degrade and become obsolete for national security . Now that all the other countries in the world have GPS satellites of their own, the intentional degradation was not required in satellites from 2000 on.